Author's Note: This was written for Obstinatrix on LiveJournal as part of a Star Trek fix exchange community. It ended up turning into my first NC-17 fic ever.

Yeah, you heard me. XD

Enjoy.

Supply and Demand

Kirk and Spock stumbled into the cramped cave, urgency pushing them forward at an almost reckless pace. Keeping his ailing first officer steady, Kirk glanced over his shoulder as they traveled deeper and deeper into the cave.

"We lost them," Kirk observed breathlessly, "How's your hand?"

Spock, still clinging to a sense of pride that he would insist did not exist in the first place, tried to lean on his captain as little as possible, "My ability to push pain into the back of my mind has been compromised and my equilibrium continues to falter."

"You said that salve is found in caves. Do we have time?"

"When speaking in terms of Earth seconds, we have precisely two-hundred and-"

"Forget I asked."

The pair continued down the long, dark path in silence. The air was getting thicker, the space around them smaller. The only source of light was the occasional patch of rock that glowed pale yellow with just enough illumination to show them the way, but that was all. They were nearly blind, Spock was quickly losing his ability to walk, and if they didn't get that natural remedy onto the Vulcan's hand in less than five minutes it would spread over his entire body and he'd be dead before he realized they'd run out of time.

And things had been going so well.

It was just a simple mission: Greet the Hollick race and sign the trade agreement. The Hollicks were peaceful, both them and the Federation were getting something from the deal, the whole mission had practically been handed to them on a silver platter.

What they hadn't counted on was the race's misplaced hatred for Vulcans. Decades ago, a small Klingon ship had crash landed on the Hollick planet after trying to take over a vessel commanded by Vulcans. Filled with petulant anger, the only survivor of the crash told stories to the Hollicks that were nothing short of slanderous, and painted a dastardly, sinister picture of Vulcans as a whole. Since the Hollick race was one of sheltered peace, they had no idea what kind of race the Klingons were and believed every word they were told. Since then they had treated any Vulcan with the utmost fear and suspicion.

So when Kirk and Spock beamed down to the planet surface with the trade agreement in-hand, they'd had no idea that the sight of a Vulcan would cause instant panic and immediate apprehension from the race's leader, Koran, and his subjects. They had seized Spock on sight, restrained Kirk, and demanded to know the "truth" as to what was going on and what kind of so-called peaceful Federation would work with such a crafty, devilish race.

It was when Kirk honestly couldn't answer their questions that the bowl of Trollim was brought forth.

There are plenty of natural resources on Hollick, but the two most fascinating were definitely Trollim and Septa. Trollim was a bright red liquid with the consistency of water that was incredibly nutritious to the planet natives, but highly toxic to anyone with Vulcan physiology. If so much as a Vulcan's fingertip came into contact with Trollim they would only have minutes left as an incredible burning infection spread over their hand and entire body before finally seeping into the bloodstream and claiming the victim's life.

But, while Trollim was great for Hollicks and lethal to Vulcans, the lesser-found Septa was exactly the opposite. Septa was a much thicker, dark green substance and a natural counteragent to Trollim. For Vulcans, it relieved the infection caused by Trollim in mere seconds, but for Hollicks just a simple sniff of the robust odor could send them into a violent seizure.

Once Spock's hand had been forced towards the bowl of Trollim, Kirk had made his move and knocked over a large torch that, in turn, set fire to the large tent they had been held captive in. The captain and first officer then escaped in the confusion and sprinted into the first cave they saw because Spock, in his never-ending knowledge, knew that Septa could only be found in the caves on Hollick.

All of that led them both to this moment, safe in the knowledge that a Hollick would never dare venture into a cave that could contain Septa but frenzied at the thought of not finding the cure in time.

Well, at least Kirk was frenzied.

His mind raced a mile a minute from worry to anger to revenge and back to worry again. Their pace had slowed so they could get a good look at the cave around them in case they ran across some Septa, but his heart was still beating as if they were at a dead run. He hated this kind of feeling, this crushing heartache, because it always meant that Spock was in serious danger. Kirk instinctively gathered Spock closer to him as he kept a keen eye out for the green remedy that would put an end to the most imminent emergency they were facing.

"Do you see anything?" Kirk asked, desperate to keep his companion talking despite the fact that he was damn near out of breath himself.

Spock's tone was still formal and in control even though his legs weren't and his breathing was labored, "I have yet to detect any amount of Septa, captain. Be assured that I will alert you when the situation changes."

"Those Vulcan eyes are always impressive, Mr. Spock, but you can't tell me that-" Kirk stopped at the sight of a slick sheen on the cavern wall to their right, "Is that it?"

Spock followed the captain's stare and nodded, "Affirmative."

He barely got the words out before his body went slack and his eyes slid shut. Kirk managed to hold onto the Vulcan and drag him over the wall, getting them situated to where Spock was sitting with his back up against the wall and his feet out in front of him while Kirk kneeled at his side.

"Spock," Kirk said loudly, grasping the half-human by the shoulders, "Spock?!"

The first officer lifted his head, clearly struggling to maintain what little consciousness he had, "It must…cover the exposed area…entirely…and be applied…in a thorough manner."

Without hesitation, Kirk reached up and swiped his fingertips through the Septa that coated the wall over Spock's head. Kirk picked up the Vulcan's infected hand by the wrist and inspected it. The infection had only spread so far as his wrist, but that was no reason to relax. Kirk went to apply the cure, only to be stopped by an insistent groan from his first officer.

"No," Spock protested, "Allow…me."

"You're delirious, Spock. Just relax, everything will be fine."

"You don't-"

Kirk cut Spock off by applying the Septa to the back of the infected hand with one smooth, insistent gesture. Spock let out a deep moan and shut his eyes, bringing his knees to his chest and looking away.

Kirk lifted his hand, alarmed, "What is it? What's wrong?"

Spock was panting now, "It…it…hurts, but it…must…be done." He swallowed hard. "Continue."

Kirk's brow furrowed. The last thing he wanted to do was add to Spock's pain, but time was short and he followed the Vulcan's instructions, resuming his task. The second the captain's hand came into contact with the first officer's skin once more, the latter tensed every muscle he had, gritting his teeth. Kirk clenched his jaw as well and tried not to concentrate on Spock's reactions. It hurt him too much to see someone so close to him in so much physical distress.

He tried to be as efficient as possible, carefully rubbing the salve over every inch of the Vulcan's afflicted skin. He was thorough, just as Spock had instructed him to be, which seemed to bring an even greater intense pain to the Vulcan because he was writhing and nearly shouting with every stroke of Kirk's fingertips against any part of his infected hand.

"Almost done," Kirk assured him, "Just this one last spot."

Kirk dutifully slid his touch over the last remaining afflicted area, careful to rub it in enough so the cure could take affect. Spock cried out, shuddering from the feeling and holding his legs to his chest with his free arm, his face still turned away.

Kirk watched as the infection on his friend's hand disappeared and Spock's breathing became normal again. He had never seen the Vulcan put on such a display before, and it tugged at his heart. Although, when Spock finally looked him in the eye, Kirk couldn't help but notice something odd. Was that a blush that tinted Spock's cheeks? Did great amounts of pain cause that reaction in a Vulcan?

"Spock…" Kirk began softly, "Are you alright?"

Spock held the captain's stare, but it was clear he had to concentrate to keep from looking away, "The Septa has served its purpose. Might I suggest we beam aboard the Enterprise to determine the next logical step in this present situation?"

In that moment, despite the dim sources of light, Kirk could see something struggling behind Spock's eyes. Normally the captain had a peculiar knack for reading Spock's body language, a trait that had served him well whenever he'd felt like testing the boundaries of their close relationship, but this time there were traces of something he couldn't quite pin down with one specific explanation. He felt the familiar tendrils of concern start to wrap themselves around his heart.

Regaining his strength and former attitudes, Spock's eyebrow twitched upward, "If I am to be intensely studied for any long term effects from the Trollim, captain, I believe a licensed medical professional would be best suited for the task or, if one is not available, Dr. McCoy will have to suffice."

Kirk realized he had been blatantly staring at Spock for much longer than necessary and stood up, unable to stop himself from clearing his throat as he took out his communicator and ordered Scotty to beam them aboard the ship. Neither would say a word until they were back on the Enterprise.

*****

A few short hours later, Kirk was strolling down the halls of his ship. His usual swagger was tightened a bit by stress, the Hollicks had maintained absolute silence since the incident and Uhura had yet to make contact, but that didn't keep him from entering sickbay with his usual authoritative presence.

McCoy sat at his desk, in the middle of filling out a report and mumbling to himself. He looked up to see who had come in and he stood up instantly when he saw that it was Kirk.

"Jim, I was just about to call you," McCoy said, something clearly on his mind.

Kirk recalled the mysterious look in his first officer's eyes from earlier that day and felt the familiar pang of worry, "Is it Spock? Is something wrong?"

"Spock's fine. I let him go back to his room a few minutes ago," McCoy glanced around sickbay to make sure that Chapel was out of earshot before he continued, "Can you walk me through exactly what happened after you found the cave?"

Kirk tilted his head slightly at the odd question, "We went into the cave, found the Septa, and Spock was mostly unconscious so I had to put it on his hand myself. Spock didn't tell you this?"

"I asked, but he insisted being Vulcan about the whole thing," McCoy replied, waving it off, "So you applied the Septa yourself."

Kirk nodded casually, "Yes."

"To his hand."

"Yes."

"With your hand."

"Bones," Kirk sighed, briefly rubbing his eyes, "if you have a point, now is the time to make it."

McCoy lowered his voice as he took a half-step closer to his friend, "What do you know about the mating rituals of Vulcans?"

Kirk shot the doctor an incredulous expression, "Almost nothing, but what does that have to do with how the Septa was applied to Spock's hand?"

"Jim," McCoy began gently, "the hands are a Vulcan's primary erogenous zone."

Kirk's was slapped in the face with a sudden realization, but did his best to try and minimize the situation, "Oh, well that's nothing. Spock was basically unconscious."

"Basically?"

"Totally," Kirk insisted, amending his previous words, "He was out. Couldn't have felt a thing. Is that all, doctor?"

McCoy nodded and Kirk thanked him as he left sickbay and started his trip back to the bridge.

Once he was free of his friend's stare, he felt his stomach wrench and turn over. The memory of what had taken place in the cave flashed before his eyes now, and it made too much sense to ignore. The way Spock had squirmed, panted, and struggled had looked like pain at the time, but now that Kirk really examined everything, he knew it hadn't been pain at all. Which could only mean…

Kirk felt a wicked tingling sensation shoot down his spine. He had been wondering what it would be like to get Spock in a position like that for a long time now, and when the opportunity had finally arrived it had flown right over his head. Granted, it had been an emergency, but remembering Spock's labored breathing, the way he grasped his legs to his chest, which must have been an attempt to hide his arousal, and his final shout of supposed "pain" was just too much for the captain to handle.

When Kirk came to the hall's intersection, he made a left.

The bridge was to the right.

He didn't care.

His pace quickened as the beginnings of a devilish plot began to form in his mind. All this time he had played coy, teased, hinted, but always took a step back at the end of the day. He did this because, even though he was quite experienced with this kind of thing, he couldn't risk making a real move on his first officer and having it backfire. As long as there was a shadow of a doubt that Spock wasn't interested, Kirk ultimately behaved himself. But now things were different. He knew enough about Vulcans to guess that if they were being touched by someone they didn't want to be touched by, no infection would keep them from bringing things to a swift halt. The logical conclusion therefore being that, even if the desire was buried deep down, Spock wanted Kirk touching him. This was a fact that had freed something in the famed captain that he had tried to keep in control, contained. But now it ran rampant through his body, and there was no use trying to reign it in now.

A playfully sinister grin flickered across Kirk's face, but he straightened it back into a neutral expression as he looked up and saw that he was outside Spock's door.

Clearing his throat to steady himself, he buzzed the door and waited patiently. He heard Spock's muffled voice grant him permission to enter, and he did.

Kirk walked into the room and the door slid shut behind him. Spock was sitting at his desk, filling out a report. There seemed to be a lot of that going around lately.

When the first officer saw that he was in the presence of his captain, he went to stand.

Kirk waved him down, "No, stay seated. I just wanted to make sure you were all right."

"Quite all right, captain," Spock answered calmly, still holding the stylus he was using to do paperwork with.

"Are you sure?" Kirk asked, folding his hands behind his back, "That Septa seemed to hurt quite a bit."

Spock's jaw tightened only slightly, "It was not the most pleasant endeavor I have had the opportunity to experience, but it was a necessary action."

Kirk was hurt for a moment, then realized that comment couldn't possibly have been meant as a jab and slowly joined Spock behind the desk, "Was it the infection that made it so painful, or does it always hurt when someone touches a Vulcan's hand?" When Spock's eyebrow arched quizzically, Kirk explained, "I don't know much about how Vulcans work. I'm just curious about what caused you to shout like that?"

Kirk's pointed stare bore down on Spock until the Vulcan broke eye contact and turned back to his report saying, "The hands of my race are especially sensitive."

"To pain?" Kirk inquired, his tone growing softer with each word.

At some point, Kirk has positioned himself behind Spock, though neither could tell when exactly that happened.

Spock's eyes were fixed on the work in front of him as he wrote, and he spoke as if he was talking to the report itself, "As I stated previously: The hands of my race are especially sensitive,"

Kirk leaned down over Spock's right shoulder so that the side of his face was a mere inch away, and let his warm breath slide over his first officer's neck. Spock stopped writing and set down the stylus, but remained motionless after that with one hand on the desk and the other on his leg.

"I've been thinking about the cave," Kirk whispered, his voice dropping an octave, "and that shout you gave when I finished rubbing that salve into your skin."

Spock said nothing, but his breath caught slightly as he felt another exhale drift across his flesh.

Kirk lifted his right hand up and reached forward until his fingertips hovered above the hand Spock had on the desk, "It seemed to hurt when I touched you…like this…"

Kirk brushed his touch across the back of Spock's hand, and Spock couldn't keep himself from shuddering.

Pressing his mouth up against Spock's ear, Kirk's voice was barely audible, "I don't think that hurts, Spock," he teased.

"Captain…" Spock managed to choke out.

"I know how it makes you feel," Kirk insisted, need and desire starting to take over his tone, "I know you had to let me do it," He brought his free hand to the back of Spock's head and slowly began to run his fingers through the Vulcan's short black hair as his voice turned raspy, "I know you came."

Kirk slid the palm of his hand over the back of Spock's and they both let out a low, guttural moan at the feeling that soared through them. When Kirk lifted his hand again and Spock tried to keep the contact, the captain felt his chest tighten with victory. His other hand slid from the back of Spock's head to his neck, threatening to slip under the pristine blue uniform at any moment.

"Tell me you want it," Kirk urged.

When he got no answer, Kirk pulled Spock out of his chair and shoved him up against the wall, pressing the length of his firm body into him. Kirk wrapped his hands around Spock's wrists and brought his arms above his head, pinning him firmly.

They were so close their noses were practically touching.

Kirk demanded ruthlessly, "Beg me."

Spock stared into Kirk's eyes, his body trembling with need, "Captain," he murmured quietly, "…touch me."

Kirk let go of his wrists and slid their palms together. White hot electricity shot through Kirk's body as he leaned his forehead onto Spock's, and they moaned together once more. Spock returned the pressure, interlacing their fingers and intensifying the sensation.

Kirk was almost dizzy with pleasure, his head swimming in warmth and arousal as he instinctively tilted his chin up to find Spock's mouth. The Vulcan turned his head at the last second and Kirk leaned back, his brow furrowing.

Their hands still locked together, Spock began to force Kirk backwards, knocking the chair off to the side in the process. Kirk felt his ass press into the edge of the desk as Spock loomed over him and brought their mouths dangerously close to each other. Aching for contact, Kirk leaned forward again only to have Spock pull back once more.

Their eyes met, and the heated frustration that Kirk radiated was fully mirrored by his Vulcan counterpart. Spock pressed into Kirk's body until the ranking officer was forced to sit on the desk. Spock then slipped his fingers out of Kirk's grip and snaked one hand behind his captain's back and the other behind his neck, taking a mercilessly firm hold of his blonde hair.

Spock's eyes took on a sinister glow, "Beg me," he ordered.

The deep timbre of the Vulcan's voice sent delicious vibrations through Kirk's body as he tried once more to unite their mouths, only to find Spock's grip on the back of his head tighten.

"Spock," he moaned, "kiss me."

Their lips crashed together with such force that, for the first few seconds, all they felt was pain. The discomfort slowly subsided as they explored each other's mouths, completely ignoring the faint taste of blood as their tongues mingled and massaged.

Kirk's hands found their way to the collar of Spock's uniform and he leaned back, pulling Spock with him until they were both lying across the desk. Only the Vulcan's feet were on the floor, and he used this advantage to balance himself as he broke the kiss and leaned back just enough to peal Kirk's uniform off of his body and cast it aside. Kirk's heated muscles tensed as he sat up enough to reunite their feverish mouths and push himself back into a sitting position. The moment he was upright once again, it was his turn to pull away in order to pull Spock's uniform up over his head and toss it the floor.

Kirk pushed himself off of the desk and into Spock's body with so much strength that it sent them rocketing back into the wall as Spock roughly captured Kirk's mouth with his. Their naked torsos slid against each other in a sinfully decadent way, and the feeling was so intoxicating that Kirk couldn't keep himself from moaning loudly into his first officer's mouth.

He couldn't take it anymore.

Without warning, Kirk flipped Spock around so that it was his front that was now pressing into the wall.

Pressing his mouth into Spock's ear for the second time that night, he growled, "Fuck the foreplay."

Spock braced himself against the wall with his hands as Kirk pulled the Vulcan's pants down to reveal a perfect, flushed ass. Kirk shoved his own pants down, relieved that his hard cock was no longer restricted. He licked his hand and quickly spread the makeshift lubricant over his erection, his first officer groaning impatiently.

Kirk seized Spock's hips and, despite the yearning of every muscle in his body to thrust roughly, did his best to take his time and ease himself inside.

Spock let out a long moan, taking a moment to adjust to the captain's size. Then he started moving his hips, urging Kirk to do the same.

The pace built quickly, and Kirk clasped Spock's shoulder to maintain his hold. As Kirk pumped in and out of him, Spock had to hit the wall to keep from screaming so loud that someone would hear. Settling into a steady, but frantic, rhythm, Kirk slid his hand from Spock's shoulder over to the back of his hand, earning a glorious, throaty moan of approval from the Vulcan. Kirk's chest and forehead was now pressed into his first officer's back, allowing for a deeper penetration that sent both of them to a new height of unbelievable pleasure.

Kirk could barely absorb how fucking good it felt to slide into Spock again and again, and to hear the grunts and gasps he earned for his work. He even began to slow down to savor the myriad of sensations that washed over him.

"Harder, Jim," Spock pleaded, "Harder."

Quick to obey, Kirk strengthened his positioning by wrapping both arms under and around Spock's shoulders and, summoning every ounce of his strength, began thrusting into Spock with an almost violent force.

The new friction was too much for of them, and Kirk bit down on Spock's shoulder as he came long and hard, his passion only heightened by hearing Spock shout of pure ecstasy from his own climax.

As the pleasure began to subside, Kirk slowed his pace until he eventually came to a stop. Neither of them moved for a long moment, they merely stood and breathed, recovering. Utterly spent, Kirk gently withdrew himself but still stayed where he was, too exhausted to move.

They stayed like this for what felt like seconds but were actually whole minutes, until Spock pulled his pants back up over his waist. Kirk did the same, and they each retrieved their respective uniform shirts.

When they were both fully clothed again, their eyes met.

Neither one moved.

The intercom chirped.

"Mr. Spock?" Uhura's voice said respectfully, "Have you seen Captain Kirk? Dr. McCoy said he left sickbay twenty minutes ago but he hasn't arrived at the bridge yet."

Kirk didn't dare break eye contact as he pressed the button for the intercom, "This is Captain Kirk."

"The Hollicks have made contact, sir," Uhura answered, "It seems they've found some new information about Vulcans and would like to re-discuss the trade agreement."

"I'm on my way."

"Yes, sir."

Kirk switched the intercom off. The fresh silence weighed heavily on both of them, each searching the other for the answer. Spock folded his hands behind his back. He seemed to be waiting patiently for Kirk to leave, like nothing had ever happened.

Kirk wanted desperately to say something, anything, but he was too afraid of saying the wrong thing to break the quiet. Reluctantly, he tore himself away from his first officer's stare and headed for the exit.

"Captain," Spock said suddenly.

Kirk stopped in his tracks and turned around. As Spock walked over and came to a stop directly in front of the captain, his eyes were cast down at the floor. Seeing Spock like that nearly sent Kirk into a panic. The Vulcan was not one to avoid eye contact under any circumstances, which suggested that this moment only had one possible ending.

After a final moment of contemplation, Spock lifted his right hand with only his index and middle finger extended, then he calmly spoke, "For Vulcans, the touching of hands in this manner is the equivalent to a kiss between humans. It is used as a customary display of affection between those who are bondmates or participating in courtship."

Okay, so maybe this moment had two possible endings.

Kirk had to fight to keep his jaw from hitting the floor as he looked down at Spock's offer. Tentatively, Kirk mimicked Spock's display, and gently touched their fingers together. The warmth that resulted from the contact was drastically different from the times their hands had met before. This was gentle, almost a tickle, and so damn pleasant that Kirk realized he must have been smiling for a while now without even noticing.

It was hard to believe that they had been in such a rough, ruthless position only minutes before, but as Kirk looked up at Spock and saw those Vulcan eyes beaming back at him with such a brilliant radiance, he didn't care much.

What happened before was sex.

What was happening now was love.