"How often have I said to you that when you have eliminated the impossible,
whatever remains, however improbable, must be the truth?"

— Arthur Conan Doyle, The Sign of the Four

"The trouble with me was, Jim, that I never could believe harm of anybody I loved."

— Willa Cather, My Antonía

Prowl turned in at the precinct gate and braked to a full stop before transforming back to base mode. His partner, outpacing him, had already performed his own transformation on the move, earning a perfunctory honk from the sentry at the gate. Prowl repressed his own inclination to scold; Tumbler had better reason than many to anticipate the end of his shift and he was hardly the only mech to commit that particular breach of protocol. The sentry's attitude was typical: Not worth a report.

And a mech who succeeds in small transgressions, Prowl's processor misquoted, will also succeed in great ones.

A few long strides caught Prowl up with Tumbler and they presented themselves together to the duty sergeant, who skimmed their end-of-shift reports before appending the Enforcer Corps' electronic seal and dumping the data to Records. "Good work today, mechs," she said gruffly.

"Thanks, Sarge," replied Tumbler. "Anything else or are we free to go?"

The older bot's doorwings flattened against her dorsal plating. "Nah, you're good, Tumbler. Message for you, though, Prowl: the investigator wants you."

Prowl suppressed an answering twitch of his own doorwings. "Thank you, Sergeant Trephine. Is he in his office?"

"How should I know?" Trephine retorted, tagging the question with the glyphs for ~need to know~ and ~above my pay grade~. But when Prowl nodded deferentially, she added with a huff from her vents, "Try the mess. Nobody's been in there for more than a centicycle since mid-shift."

"Thank you, Sergeant," Prowl said again, raising his doorwings in salute before turning away. Tumbler flicked Trephine a more casual version of the gesture and fell in beside his partner. Prowl eyed him askance. You don't need to come with me, he sent privately.

But I'm hungry, Tumbler answered, patting the armor that covered his fuel tanks. I burned through this morning's cube decicycles ago and somebody kept me working straight through my mid-shift break —

Crime waits for no mech, Prowl responded automatically, processor occupied with calculating the possible reasons for Investigator Jazz's summons and the ramifications of allowing his partner to pass before the mech's deceptively inattentive optics. Rollbar expects you —

Tumbler's field discharged a crackle of static through his: ~low blow~. A fine Guardian I'd be if I collapsed from lack of fuel on my way home, he sent. Don't deny me my allotted rations, Prowl. Thou shalt not throttle the intake —

— of the drone who processes the energon, Prowl joined him in concluding, recognizing the futility of further argument.

Truth be told, Tumbler's presence comforted as much as it concerned him. The other mech knew better than to draw the investigator's notice, but his readiness to back his partner up warmed Prowl's spark. His rapidly spinning processors slowed, discarding wild improbabilities and weighing facts. The Joint Federal-Metropolitan Task Force on Sparkling Welfare was not due to meet again for several cycles, and though the investigator had been haunting the corridors of the precinct since the last session, his movements exhibited no significant patterns. Of late he had made nothing but social requests of Prowl, commandeering him to play tour guide among the sights of Praxus or (more commonly) its many oil houses. If Prowl's fellow officers drew away from him, comms crackling with private judgments about his intercourse with a minion of the Office of Cultural Investigation, Prowl soothed himself with the knowledge that he was doing no more than his duty. Good service is its own reward, he had told Blockade all those cycles ago when the mech had recruited him into the conspiracy the investigator had been sent to unravel. Prowl required no bot's approbation of actions he knew to be correct.

He vented evenly, timing his atmospheric circulation to his steps in a meditative technique to settle his systems. He no longer had the excuse of unfamiliarity to run on high alert in Jazz's presence, having been among the first to meet the investigator upon his arrival in Praxus. "He asked for you by name, Patrol Officer Prowl," Commander Blockade, carefully formal in his office, had said when informing Prowl of his assignment. "You will be excused from your normal duties to attend all meetings of the task force; in addition, you will hold yourself at the investigator's disposal for any other tasks he might assign. He will coordinate with your precinct captain to ensure that your shifts are covered and that you are compensated for any overtime." He had given Prowl a moment to absorb this information, then leaned forward with his digits steepled on the desktop between them. "You have a sterling record, Officer Prowl. Praxus is well served by bots of your stamp. Do your city and your comrades proud."

"Yes, sir," Prowl had responded, caught between gratification and dismay.

Tumbler had publicly commiserated with him about having to trail around after a stylus-scraping Iaconian bureaucrat, but privately reassured him that he was equal to the task of matching wits with a cultural investigator. "You're the smartest bot I've ever met, Prowl," he'd said, "and you know the nanocycle you pass for sergeant, Tactical's going to snap you up like a turbofox on a retrorat." He clouted Prowl bracingly between the doorwings. "Even if OCI's got an inkling about you, or you and me and the others, I'd back you against the Senate's best and brightest any shift." And when Prowl had shaken his helm, Tumbler had grabbed him by the back of the neck and pulled him in, chevron to chevron, and sent ~trust/loyalty/certainty~ in glyphs that all but radiated into the infrared.

In the face of such faith, how could Prowl doubt?

He ran one last quick diagnostic that returned all systems nominal, cleared his caches, and opened the door the street patrol's mess. As Sergeant Trephine had said, the room was practically and uncharacteristically vacant: no line at the energon dispensers, and the few Corpsbots present clustered at a table to the right of the entrance, downing their cubes with businesslike haste. The left side of the room was in sole possession of a silver minibot, visor dim, leaning back in his chair with his pedes propped on a table, to all appearances peacefully recharging.

Prowl didn't believe that for a nanocycle.

Tumbler's field nudged his encouragingly as his partner barged toward the energon dispensers like a mech facing imminent shutdown. Maintaining his own deliberate pace, Prowl crossed the room to Investigator Jazz's table, aware of the covert scrutiny directed at his back. His doorwings rose minutely, as if to shield him from his fellows' disapproval. Despite his devotion to the cause, he could not always suppress the processes that whined I am just doing my job! in the face of censure. It's the job that matters, he reminded himself — both his jobs, the little work of serving Praxus and the greater one of serving Primus.

He turned his regard away from the onlookers to focus on Jazz. The investigator gave no sign of noting his approach, comms offline and field dormant. The only indication of consciousness was a faint buzz of sound that resolved into a tinny strain of melody as Prowl drew closer — a protest song from the Quintessan occupation.

"My thoughts, they are free; no mech may compel them.
As Seekers they speed, my spark to impel them ..."

Prowl winced, browplates drawing down as he calculated the volume at which Jazz's internal playback would have to be set to be externally audible. Unless, of course, it were merely a ruse to put listeners off their stride — this was not the first time Prowl had heard Jazz leaking music during an interview or a meeting. He drew himself to attention. "You wished to see me, Investigator?"

The tune broke off as Jazz's visor lit. "Officer Prowl!" he drawled, swinging his legs off the table and gesturing Prowl to a seat. "Take a load off! What's the word on the street?"

"Proceeding in excess of posted speed limits remains illegal," Prowl said as he took the offered chair, "popular opinion in some quarters to the contrary."

Jazz chuckled. "Can't say as I blame 'em. Awfully low, your posted limits."

Prowl inclined his helm. Judging by the lines of his altmode and the high-performance thrum of his engine, the decorous pace Jazz set when driving with Prowl was not all he was capable of. "I understand that the Praetor's office is considering several petitions to raise those limits on the beltways," he said. "Do you wish to register an opinion?"

"Nah, 's not my city," Jazz demurred with a sardonic tilt to his mouth. "Who'm I t' tell y'all how to run it?"

Behind Prowl several chairs scraped across the floor as their occupants rose to leave. Jazz's field expanded, as if daring Prowl to take up the challenge, but Prowl held his steady. "Objectivity is difficult to achieve when the question is personal," he said.

Jazz's visor flashed with amusement. "Oh, undoubtedly," he said, his accent flattening to Iaconian standard. "Any drivers in the Praetor's office?"

"Praetor Tombac strongly supports the development of public transit," Prowl replied, lip-plates curling ever so slightly.

"Bless his spark," Jazz said, voice reverting to its usual drawl. "Quiet shift, then? Wasn't sure I'd catch you; thought you might be pullin' overtime." Prowl blinked at him, nonplussed — surely the investigator had access to the precinct's duty roster? — and Jazz clarified, "Y'know, for th' concert."

Ah. "No," Prowl replied regretfully. When the celebrated musician and philosopher Diaton had emerged from seclusion to announce a performance to benefit the victims of the latest Kaonite mine collapse, Prowl had considered volunteering for the security detail and a chance to attend an event he'd never in a million solar cycles be able to witness otherwise. But his lack of seniority reduced the odds of being assigned to the amphitheater in the Crystal Gardens to an equally astronomical improbability, and he had duties nearer home to occupy his time. Still, the investigator should have known his schedule. Unease set Prowl's processors humming, but he kept all curiosity from his voice as he asked, "Do you require my services this evening?"

"Nothin' like that," Jazz said, waving off the idea of duty with his usual nonchalance. "Jus' thought you might be a fan. Diaton was a big noise back in th' day — before your time, maybe?"

Now Prowl was sure Jazz was playing with him, but to what end remained unclear. Every Praxian sparked in the last gigacycle revered Diaton, the city's most sublime exponent of crystallody. In her youth, it was said, she had drawn tears from all five faces of a Quintessan ambassador with her rendition of Concord's "Paean," and even bootleg recordings of her mature performances could enrapture the spark as well as the audial. At the height of her fame, however, she had retired to pursue an anchorite's vocation, occasionally publishing the fruits of her reflections to as much acclaim as she had earned on the stage. "Diaton secluded herself before I was sparked," Prowl acknowledged, "but I'm familiar with her recorded work, of course — "

"And her Aphorisms," Jazz muttered. "Can't get through a conversation here without having one of 'em thrown at me."

Prowl lowered his doorwings in a half-truthful expression of sympathy. Diaton's Aphorisms were a school text and without doubt her most accessible work, though in Prowl's opinion not her most profound. "I prefer the Apophasis myself," he said. "I find it rewards rereading."

"Title like that, I'd think it'd reward not being read at all," Jazz retorted.

Caught off guard, Prowl laughed, doorwings flaring, and Jazz grinned at him with apparently genuine good humor. In moments like these Prowl deplored most the circumstances that placed him and the investigator on opposite sides in the covert battle for the soul of Praxus. Despite his casual demeanor and nonstandard accent, Jazz was well-educated, steeped in the culture his office so stringently regulated. Music was his great passion, but when the mood took him he could converse intelligently about any of the arts. Yet even as Prowl's field matched frequencies with Jazz's, an ever-active security subroutine sounded its usual warning: This mech is dangerous; do not reveal yourself to him. Schooling his features to polite appreciation of the investigator's joke, Prowl folded his doorwings. "Shall I fail to procure a copy for you, then?"

"Nah, I'm pretty sure I can avoid it for myself," Jazz replied. "Got something for you, though, if you're free this off-cycle."

Prowl's spark contracted in its casing and he quickly called up his calendar and the algorithm he had developed to schedule his social engagements with the investigator. It would not do to be at the other mech's beck and call outside of work, but neither could he risk losing the opportunity for soft intelligence-gathering their convivial outings afforded. "My neighborhood association meets this evening," he said cautiously. He served as the Corps' representative to the group but was not scheduled to speak; depending on what Jazz had in mind, Prowl could as easily plead his excuses to the chairbot as to the investigator.

Jazz's browplates rose. "Still? Even with all the hoopla?"

"It is unlikely to be as well attended as usual," Prowl admitted. The concert's organizers had persuaded Diaton to permit a simultaneous audio-only broadcast from the Crystal Gardens to several ancillary venues, so that those who could not procure tickets to the event itself could still hear her perform and make voluntary donations to the relief fund. Many of Prowl's neighbors had asked him when the gates to those locations would open, and he and Tumbler had spent much of their shift dispersing the premature queues blocking traffic in the surrounding streets. The punctilious chairbot, Prowl reflected wryly, might well be the only mech in the neighborhood beside himself even to remember the association's meeting.

"Doubt they'll miss ya, then," Jazz replied. He pulled something from his subspace and tossed it at Prowl in a high, lazy arc. "Here."

Prowl snagged the object — a data chip — deliberately fumbling the catch to give himself time to engage his secondary firewalls. The chip was heavy for its size and oddly ornamental, slim gilt and cobalt threads glittering within its dark crystal housing. Perhaps it contained passcodes for some exclusive club. Prowl groaned inwardly as he inserted the chip into one of his wrist dataports. He wore his enforcer's colors proudly, but they could draw unpleasant attention at the highest as well as the lowest levels of Praxian society. A beat patrolmech would be as out of place in a Tower lounge as in an undercity dive — unlike the investigator, whose frame could pass anywhere. Prowl accessed the chip's outermost data layer, his antivirals and intrusion-detection routines scanning for malware as thoroughly as he dared. Too great a delay and Jazz would realize what he was about, which would at best insult him and at worst set them at overt odds.

But Prowl need not have worried, for the label alone was sufficient to bring his lexical processors to a halt long enough for his security protocols to declare the chip clean.

ADMIT ONE

The Arts Council of Praxus
and the Metropolitan Crystal Orchestra
present
a concert for the benefit of
the Kaonite Mine Disaster Relief Fund.

Featured soloist: Diaton ...

Nanocycles passed before Prowl wrenched his awareness outward to stare at Jazz. "How did you — "

Jazz shrugged, broadcasting smug satisfaction. "Oh, I know a bot who knows a bot," he said. "Mind you, we'll probably be perched up on a light stanchion, but we'll be there." He pulled a matching chip from his subspace and flicked it into the air, smirking at Prowl's confusion, his expression sly and triumphant and somehow familiar.

Prowl rebooted several stalled analytical subroutines and shook his helm. His doorwings trembled with excitement his cortex could not wholly repress and he knew that his field was shot through with anticipation at this unexpected opportunity. "I never thought ... this is ... "

Jazz's smile widened, and that weird sense of recognition teased more strongly at Prowl's memory. "I b'lieve the phrase you're lookin' for is, 'Thank you, Jazz.'"

Realization broke over Prowl like an unexpected wash of solvent. Jazz's attitude — he'd seen Tumbler look just so at Rollbar when presenting him with a new toy, heard his own Guardian similarly prompt his thanks before his first driving lesson. He might even have worn such a smile himself when he drew Tumbler through the warehouse door to show him the device that would free them to fulfill the deepest desire of their sparks. And the chip — even the cheapest tickets to the benefit were priced beyond the means of a low-ranked civil servant and their street value was colossal. Rumor had it that scalpers were demanding ten times face cost, minimum. He could never repay Jazz for this — it was a gift that sought no return —

No: demanded no return.

Prowl's vents hitched. He must decline. Either the chip was a bribe from an adversary seeking to subvert his allegiance to the Corps or the largesse of a friend to whom his allegiance was simply assumed. He could not — dared not — place himself under such an obligation. Not to Jazz. Not the Office of Cultural Investigation and its Senatorial masters, with their dream of a world in which all loyalty lay with the state.

He withdrew the chip from his dataport and placed it on the table. "I'm sorry," he said. "Thank you, Jazz, but I cannot accept your invitation."

Jazz reared up in his chair, all pleasure bleeding out of his field. "Why the Pit not?"

"As I said, my neighborhood association meets tonight — " Prowl began, cursing himself for the weakness of the excuse, on which Jazz pounced like a cybercat.

"Ditch 'em — you said it yourself, no one's gonna show." The minibot leaned across the table, his field pressing into Prowl's. "Or send a sub. Your partner'd fill in for you if y' asked, wouldn't he?" He glanced over his shoulder-guard at Tumbler, draining the last of the energon in his cube before placing it in the recycler. His back was to them, but from the set of his doorwings Tumbler was following their conversation closely.

Prowl's spark pulsed unevenly. The last thing he wanted was to bring Tumbler (and with him, Rollbar) under Jazz's scrutiny. He drew himself up to his full height, catching and holding the investigator's gaze. "It is my duty," he said firmly. "I cannot shuffle it off for the pursuit of pleasure."

Even to his own audials he sounded like a pompous gasbag, and Jazz laughed at him. "Listen to yourself, mech! It's a neighborhood association meeting, not an address to the fraggin' High Council."

"It is my responsibility," Prowl replied, sticking to his point gamely if lamely. "I cannot abdicate it."

"Yeah? Says who?"

Prowl kept his optics locked on Jazz's visor, but his doorwings' sensors told him that Tumbler was making his way toward them, no doubt primed to intervene. Desperation lent speed to his processors and his cortex provided an answer to the investigator's rhetorical question. "Diaton."

Jazz's visor winked. "Say what?"

"Diaton. 'Hot or cold, full or empty, living or dying, do your duty, for Primus requires of you even your death.'" Prowl managed to dredge up a smirk. "The Aphorisms, of course."

"Of course," Jazz echoed, and threw up his servos. "You're gonna turn down the chance to hear the femme play just so you can live out one o' her li'l sayings." His tone was cutting. "Hate to break it to ya, Prowler, but she ain't never gonna know."

"But I will," Prowl said quietly.

Jazz's helm jerked back; catching himself, he slumped in his chair as if that was what he'd meant to do all along. Prowl leaned forward, following up his advantage. "While I wear these colors, everything I do sets an example," he said, sweeping a servo down his chassis. "I do not have the license to indulge my private desires at the expense of the public good. If I fail to fulfill my obligations, I undermine not only my own effectiveness, but also that of my comrades." With a single digit he pushed the chip back toward the investigator, though he allowed his genuine regret to color his field. "Your offer was most generous. I am truly sorry to refuse it."

Jazz scrutinized Prowl, helm tipped to one side, then turned to take in Tumbler, meandering purposefully toward them, and the sudden buzz of conversation that failed to conceal the avid interest of the room's other eavesdroppers. A series of emotions flickered through his field too quickly for Prowl to catch, settling finally into something wry and sour. "Can't say as I've ever had to worry about that," he said, waving at his own unmarked frame. "Still, I get it." He swept the chip back into subspace, pulling in his field with it. "You're an honorable mech, Prowler. Don't meet many of those in my line of work." He stood and smiled. "Makes a nice change." Tossing a salute at Tumbler, he ambled to the exit, music leaking from his speakers once more.

"My thoughts, they are free, no mech may compel them.
As Seekers they speed, my spark to impel them.
No cell can contain them, no force field restrain them.
Let none disagree: my thoughts, they are free!"

Prowl watched the investigator out the door, heedless of the optics canted in his direction, until Tumbler deliberately stepped into his line of sight. "Gonna get a cube now?" he asked.

Prowl's tanks were half-drained, but the thought of the precinct's bland mid-grade made them lurch. "No, I'll refuel at home."

"Then let's roll," Tumbler said, flashing him a cheerful grin that barely disguised the tension stiffening his jaw.

It was a relief to drop into altmode and drive away from the station, away from its pricked doorwings and electric currents of gossip, away from the investigator's subtle devices. Gift or graft or sop or ... ? Prowl followed close in Tumbler's wake, letting his partner set their pace, taking solace in the mech's eagerness to reach their destination. As they exited the beltway to thread a path through the commercial district that bordered their neighborhood, Tumbler pinged Prowl's comms. I was thinking of taking Rollbar to the park before we head home. Want to come?

Of course! Prowl replied. Spending time with the youngling who called him patruus always lightened his spark, even as it filled him with longing for the cycle when one would call him Guardian. I'd be delighted.

He trailed Tumbler down a quiet side street to park before a building whose brightly painted colonnade, hung with baskets of well-tended crystals, did much to enliven its worn façade. The atrium within rang with the voices of younglings at play, dodging between the pedes or scaling the frames of their elders with affectionate fearlessness. Tumbler and Prowl exchanged greetings with the preoccupied mechs and femmes, Guardians all or the cadremates of Guardians. Praxus no longer subsidized sparkling care for its citizens, instead funneling such funding as remained available to the public crèches raising unbonded younglings. Since private tutelage strained the means of most bots, those who could formed cooperatives like this one to share the burden and privilege of raising the next generation. Tumbler spent most of his off-cycles here and Prowl donated as much of his own time as his duties permitted, banking good will against future need.

Tumbler strode across the atrium to a sand-table surrounded by small frames, calling as he did so, "Where's my Rollbar?"

"Guardian!" One bright chevron popped up from among those bent over the table, and a small grounder barreled across the tessellated floor to throw his arms around Tumbler's leg. "Here I am!"

"There you are!" Tumbler agreed, hefting the little mech into the air and then clasping him to his chestplates. "Have you been good today?"

"I was good," replied Rollbar, laying the side of his helm against the armor over Tumbler's spark chamber. "I was very, very good."

Tumbler grinned abstractedly, evidently confirming that statement via private comm with one of the cycle's caretakers. "Then I have a treat for you," he said, caressing Rollbar's doorwings. "What say you and I and Patruus Prowl spend a little time at the park before you refuel and recharge, hm?"

"Yes! Yes, please!" Rollbar bounced in his Guardian's arms, craning his neck in search of Prowl and smiling brightly when he caught sight of him. "Hello, patruus!"

Prowl returned the smile and laid a gentle hand on Rollbar's helm. "Hello, nepos," he said. "I'm very glad to see you."

"Me, too," said Rollbar. He wriggled and pushed at Tumbler's chest. "May I get down? And walk to the park?"

"I don't know," replied Tumbler, the doubt in his voice belied by a teasing glimmer in his field. "That's a long walk for a little mech."

Rollbar's engine revved indignantly. "I'm not so little! Not any more! I'm — " he held his digits a span apart — "this much bigger than I was last cycle. Magistra Platina measured me!"

"All right, not so little, then," Tumbler agreed and allowed Rollbar to slither down his chassis to the floor. "Keep hold of my servo and don't pull, and we can all walk to the park together."

Rollbar clapped and cheered, then snared one of his Guardian's servos in his and waved imperiously at Prowl. "Take my servo, Patruus Prowl, so you don't get lost."

"Thank you," Prowl answered gravely, folding the offered digits within his own. He glanced over the youngling's helm at Tumbler, intending to share a fond smile with his partner, but the other mech's gaze was unexpectedly grave above the curve of his mouth. Prowl tilted his helm quizzically, but Tumbler looked down at his sparkling and allowed the small mech to pull them all toward the exit.

Rollbar chattered incessantly and sometimes nonsensically to his Guardian throughout their short journey. At this stage of his development, his linguistic abilities still outstripped his ratiocinative powers and Prowl's processors occasionally strained to keep up the with the youngling's leaps of logic. But Tumbler let Rollbar ramble on, correcting only the most egregious errors, and Prowl himself said nothing, content to hold his nepos's servo and help Tumbler swing the mechling between them until they arrived at the park. Rollbar immediately pulled free and ran ahead, exhorting his Guardian to hurry, hurry!

The park, like the crèche, was a common resource, the site donated by a civic-minded landlord and maintained by volunteer labor. It was nothing to the grand municipal gardens where Diaton would play, but cleverly designed paths wound between outcrops that blocked the sights and sounds of the surrounding neighborhood, dipping into hollows chiming with crystals and rising on small spans to cross quicksilver streams. The place held no playground equipment, but younglings could make do with spurs to climb and crannies in which to hide or make forts. Prowl heard the shouts of a group engaged in a game of seek-and-find and recognized the voices of several of Rollbar's crèche-mates. The mechling himself, meanwhile, made straight for his favorite spot, a squat pillar with a cup-like depression at its apex, around whose rim bloomed a ring of tinted crystals: dawn red, cyanine blue, and methyl yellow. "Up, Guardian, up!" Rollbar demanded, rising onto the balls of his pedes and straining to reach the lip of the cup. "Please!"

Tumbler laughed and swung his sparkling up to sit in the center of the ring, while Prowl took station on the opposite side. Together the two mechs coaxed the crystals to life, tapping and stroking the glossy growths until they sang. The nursery tune Prowl and Tumbler played was not even a distant echo of the fantasies of Diaton or Concord, but Rollbar was no less appreciative an audience than theirs, singing along and occasionally making clumsy attempts to strike a note from a spire within his reach. As Prowl focused on keeping time with Tumbler, his pulse gradually synchronized with the beat of the music and his spark radiated a gentle ardor through his chassis. Words accompanied the warmth, a quotation from the Apophasis on which he often meditated: I will leave behind all knowledge and love that which I cannot conceive, for love may reach to Primus in this life, but not knowledge ...

His musings were interrupted by a ping from Tumbler. Prowl — about what happened in the mess ...

Prowl stiffened, though his digits did not falter on the crystals. Rollbar loved this spot in all innocence, but his elders had their own reasons to prefer it. Playing music made recourse to private comms unremarkable and a seeming-careless overstimulation of the crystals could fill the ether with interference, rendering long-range eavesdropping impossible. Still, Prowl was not eager to discuss Jazz's invitation with his partner, privily or no. I handled it, he replied. No further intervention will be necessary.

Tumbler broadcast a glyph of negative agreement, accepting the point without conceding the argument. The investigator — he's had his optic on you ever since he arrived.

Prowl's doorwings half-rose to a guard position, their shadow falling across the tip of Rollbar's chevron. He will not discover us, he sent reassuringly. I have the advantage: I know why he is here, but he only suspects the Corps is compromised.

That had been an unpleasant revelation. Jazz had sat without comment through a kilocycle's worth of speechifying and sniping by the task force's members, all of them more eager to promote their patrons' influence than to foster sparkling welfare or even prevent any further deaths in the public crèches. Prowl, taking the minutes, had covertly shuddered at their indifference as he marveled at the social engineering required to produce such utter ineffectuality. The dreaded cultural investigator himself had seemed more interested in sampling Praxus's nightlife than cracking down on social deviance, proving a pleasanter companion than Prowl could have imagined. He had begun, not to relax around Jazz, but to rate him without reflexive fear for the conspiracy and its dependents, even to cautiously enjoy his wit and verve.

And then, after a particularly content-free meeting during which the investigator had not bothered to conceal his boredom, humming phrases from Metronome's Requiem loudly enough to earn him sour side-optics from his neighbors, Jazz pulled Prowl aside. "I need ya t' look up some cold cases," he said, transmitting a daunting string of file numbers. "Summarize 'em for me and flag any common elements."

"Yes, Investigator," Prowl replied. "When would you like this précis?"

Jazz shrugged, but his visor glimmered mischievously. "Oh, end o' your next shift's fine. My boss thinks my reports are a lil' light on data; gotta toss him a strut."

Prowl immediately began downloading the required files from the Corps' database. The investigator's deadline would leave him barely enough time to complete the report without overclocking his processors, and that only if the rest of his shift went absolutely smoothly. "Of course, sir," he said, meeting Jazz's gaze expressionlessly. "If you will excuse me?"

He'd ended up overclocking anyway, running the analysis twice to confirm its dismaying conclusion. Unsurprisingly, the cases involved the deaths or disappearances of sparklings from Praxus's public crèches; more surprisingly, all had occurred megacycles ago — and in sixty-five point seven percent of the cases, the investigating officer had been then-Sergeant Blockade. Prowl could do nothing but flag his commander's name among the other commonalities he noted, none of them as damning, and contact his blind drop with an urgent update regarding the investigator's line of inquiry. Jazz had accepted the report without comment on its substance and stood Prowl a can of oil for his trouble ("Data-mining's thirsty work!"), as Destroyer-may-care as ever he was.

But thereafter Prowl was convinced that the investigator's bored indifference concealed dire conjectures, and his idle manner a program to strike at the very heart of the conspiracy to preserve Guardianship in Praxus. None of its leaders, nor its members beyond Blockade and Tumbler, were known to Prowl, but he strongly suspected that his commander was a linchpin in the machinations that abducted sparklings from the public crèches, camouflaged their origins, and matched them with loving (and rigorously vetted) Guardians. Blockade's exposure, Prowl's calculations suggested, would debilitate the conspiracy, if not doom it outright. So Prowl had redoubled his counterintelligence efforts, throwing what dust he could in the investigator's optics, but in the moonless watches of his shifts he feared that it would not be enough to save his mentor. His only consolation in those dark moments was that he himself remained unsuspected, free to defend his partner and his nepos with all the considerable resources of his mind and spark.

For surely not even Jazz could simulate camaraderie so cunningly that a trained enforcer could not detect the lie.

But Tumbler was still transmitting unease on their private channel, though nothing of it showed in his demeanor. The more he associates with you — the task force is one thing, Prowl, but all those off-cycles you spend with him —

No more than I do with you, or any other friend, Prowl replied, impatience leaking into the line despite his attempt to quell it. Tumbler's Guardian protocols, he reminded himself, were running hot and the mech was still new to managing their protective impulses. Prowl packaged a dataset on the frequency and duration of his contacts with Jazz and forwarded it to Tumbler. As you can see —

But Tumbler bounced the information back to him unread. That's not what I mean.

Prowl's doorwings twitched at the concern in his partner's field as if at some passing interference, but he reined in his irritation as he caught the subtext of Tumbler's anxiety, his apprehension not for the conspiracy or even for Rollbar, but for Prowl. Why me? After all their shifts on the beat together, surely Tumbler knew that Prowl could handle himself. Still, the Corps had good reason to assign patrol officers in pairs; even a doorwinged frame's sensor suite had its blind spots. I've been careful, Tumbler, believe me, he sent. I go nowhere unarmed and keep to public venues —

All of them perfectly respectable, and you get your own cube and filter your energon twice when you drink with him, Tumbler interrupted, finishing Prowl's sentence with uncanny accuracy. That's not what worries me, Prowl. You're not going to set yourself up to get hacked in an alley.

Then what is it? Prowl demanded.

Tumbler said nothing for a moment, leaning forward to tap his chevron against his sparkling's and earning a giggle from Rollbar. I just — he began, then halted, the open channel transmitting nothing but his disquiet. Prowl lifted a browplate and waited until his partner continued reluctantly, You don't have a lot of ... close associates.

I fail to see what that has to do with the matter, Prowl replied flatly. My record is exemplary; my cover is secure —

Primus dammit, Prowl, I don't doubt that! Tumbler snapped, and the unaccustomed profanity brought Prowl up short, his digits stumbling discordantly upon the crystals. But the investigator's playing the good enforcer with you, and just because a bad one isn't looming behind him doesn't mean it's not a Pit-effective tactic! His own digits didn't miss a beat, catching Prowl's error and correcting for it, modulating the tune into a new key. I'm not worried about him getting into your helm. I'm worried about him getting under your mesh.

Chastened, Prowl let an apology flow wordlessly back across the line. Tumbler's anxiety was exaggerated, of course, but not unfounded, and Prowl did their partnership no service by dismissing his friend's concern. I will be careful, I promise, he said, adding with an attempt at self-deprecation, I always am, you know.

Tumbler shook his helm. You can't be too careful around this mech, Prowl. I mean it.

Prowl tamped down a renewed surge of annoyance. Understood, he sent, though in truth Tumbler's misgivings confused and upset him. In search of a change of subject, he checked his chronometer and noted with some surprise how much time had passed since they had entered the park. He would have to put pedal to the metal to reach the neighborhood's community center punctually; in addition, it would soon be time for his nepos's end-of-cycle energon. Sending a horological ping to his partner, he tapped Rollbar's shoulder-guard. "Perhaps it's time for all good mechs to refuel?"

As he expected, the youngling emitted a wail of protest: no, please, just a little longer! But Rollbar was hungry enough that when Tumbler, following Prowl's lead, lifted him out of the crystal ring, he immediately began to beg for a sip of his Guardian's off-grade in addition to his own ration. Those negotiations carried them to the park entrance, where Prowl raised his servo in awkward farewell. "I must be off," he said. "Primus keep you.,"

"But Patruus Prowl," Rollbar protested, "won't you take your energon with us?"

"Not this cycle, I'm afraid," Prowl answered. "I have a meeting — "

— and his vocalizer glitched as he realized that he was offering the same facile excuse to Rollbar, to a sparkling in the presence of his Guardian, that he had to Jazz. Prowl's spark guttered, darkening his field with mortification as he raised his stricken optics to Tumbler's. His partner deserved better than to be warded off with pretexts, and his nepos — ah, Primus, his nepos! — needed an example of probity and candor, not this ... double-dealing. Doubt twisted Prowl's fuel lines into familiar knots: how long could he play the adversary's game without becoming what he countered? How long could a liar defend the truth?

(Sop or graft or gift ... ?)

But Tumbler met his troubled gaze with wry acceptance, laying a servo on Rollbar's helm. "Your patruus has work to do," he told his sparkling, "and Primus says we must always do our duty, no matter how hungry we are."

Rollbar frowned as Prowl blinked, startled, semantic protocols parsing this remark for sarcasm and finding none. "But you have to refuel when you're hungry!" the mechling insisted. "Otherwise you might crash!" He held out his servos to Prowl, optics round and pleading. "Come and refuel with us, patruus. I don't want you to crash."

Prowl's spark blazed anew, swelling fit to breach its casing. He knelt down and took Rollbar's servos in his. "I'll refuel on the way to my meeting, I promise," he said, nudging the youngling's anxious field with his own, scrupulously laved of all distress. "And maybe afterward I might bring you an energon treat to share?" He glanced up at Tumbler. "With your Guardian's permission?"

For a moment he feared he had misstepped, as Rollbar whirled to fling his arms around his Guardian's knees and plead for the treat with an electric, nonverbal surge of greed and delight. Tumbler cocked a weary browplate at Prowl. "Someone," he said, "is going to have either a backlogged tank or a cityformer's altmode if his patruus keeps spoiling him." But before Prowl could apologize or withdraw his offer, Tumbler smiled down at Rollbar. "Very well. One energon treat. To share. What do you say?"

"Thank you!" crowed Rollbar. He spun again, butting his helm against Prowl's abdominal plating as he wrapped his arms as far as he could around the larger mech's waist. "Thank you, patruus."

"You're welcome," Prowl responded, gently returning the embrace. Then he disentangled the sparkling's arms from his chassis and, lifting the happily wriggling frame, stood to pass him back to his Guardian. "Until later." ~Yes/no?~ he added privately to Tumbler, still somewhat uncertain of his welcome.

~Emphatic affirmative/pointless query~ came the immediate response, with the field-resonance equivalent of a teasing slap to the helm. Prowl's mouth worked, caught between affront and relief, and Tumbler grinned at him. "Just one treat, please," he said, mock-serious. "There'll be no backlogged tanks on my watch."

"Could I have a cityformer's altmode?" Rollbar asked, obviously entranced by the prospect.

Tumbler laughed. "We'll see, my spark. We'll see."

Prowl stepped into the street and transformed, flashing his taillights in response to Rollbar's enthusiastic wave before departing. He drove with all decorum to the corner, then accelerated once he was out of his family's sight. Only a generous interpretation of the local speed limits would permit him to refuel without being late to his meeting, but he would keep his word to Rollbar. Systems were made for bots, not bots for systems, his own Guardian had often chided him when Prowl's conscientiousness had shaded toward scrupulosity. He rejected any self-serving implementation of that dictum, of course, but when the choice lay between a promise to a sparkling and a minor infraction of traffic rules, or when the aims of the state conflicted with the laws of Primus, Prowl knew his duty, and it pleased him to carry it out.

Hot or cold, full or empty, living or dying ...

He cornered again, feathering the turn with a delicacy that he suspected would do even Jazz proud, and pulled up at a drive-through energon dispensary. Its mid-grade was even blander than the precinct's, but Prowl's tanks accepted it contentedly. Only love may reach to Primus, he thought, and surely that love would see his partner and his nepos through to an era of renewed freedom, and himself to the fulfillment of his spark's desire.

Only love ...

Author's Note: The alert reader will notice ... similarities of expression ... between Diaton and both Marcus Aurelius and the Ancrene Wysse, and between Prowl's Guardian and the Bible by way of Madeleine L'engle. Great minds think alike. And every planet needs a version of "Die Gedanken Sind Frei," even if every planet doesn't have a Pete Seeger to sing it.