A/N: The title is derived from "mnemonics," the study of techniques to improve memory. Story will have 9 chapters.

Disclaimer: Not mine. Thanks to 29Pieces for beta reading! ^_^

Chapter 1: Lost and Found

Dean didn't push the speed limit as they headed home after the case in Grand Junction. He needed the highway to stretch out as long as possible so he could just stay in that headspace of focusing on the sound of the Impala's rumble devouring the road. He didn't want to think about that kid he'd failed to save, or the nephilim child waiting for them back at the bunker. Dean needed a win but he was tired of chasing it, and in this moment, he let himself feel like he was fleeing instead—from the grief and pain, from the weight of Billie's pronouncement that he and Sam were important.

If they were so damn important, why couldn't he save those who were important to him?

The tires ate up the miles. Sam slept in the passenger seat. And Dean's gaze bored holes into the void of night as dark and empty as the void in his heart.

He stopped for gas just over the Kansas border, a little before midnight. Sam woke, and got out to stretch his legs.

Dean leaned against the Impala, one hand holding the gas nozzle in place as it guzzled fuel into the tank. His eyes roved around aimlessly, mostly out of habit and not because he was paying any crucial attention to his surroundings. Until a glimpse of tan caught his eye. Dean's focus snapped to a figure across the road from the gas station, and his lungs suddenly forgot how to breathe. The trench coat, the dark hair… No, it was impossible.

This wouldn't be the first time Dean had seen hallucinations of Cas, though in the past they'd been born of guilt more than grief. Still, Cas was dead, so whatever Dean's brain was conjuring right now was just a cruel joke.

And yet he couldn't bring himself to look away. Cas looked up and down the street a few times, almost as though unsure of which way to go. So, what, this vision of Cas was supposed to be some sort of representation for how lost Dean currently felt? He didn't need this shit.

"Dean? What are you…" Sam had been walking toward him but stopped, and Dean heard him suck in a sharp breath. "Is that…?"

Dean swallowed hard. "You see him?" he croaked out, afraid the answer would be no—afraid it would be yes. He didn't dare take his gaze from Cas for a single second, not even to check his brother's expression in order to gauge what was happening, if maybe he was just losing his mind.

"Yeah, but how—"

The confirmation was all Dean needed to lurch away from the car and start across the street. Cas was already turning down an alley and walking away from them. Dean quickened his pace.

"Dean, wait!" Sam hissed, running up behind him. "What if that's not him? What if it's some kind of trap?"

Dean clenched his fists tightly. Then he would rip apart anyone who had the gall to use his best friend's dead face to screw with them.

But if it wasn't, if it really was…he didn't have answers as to how that could be. They'd burned his body, for crying out loud. But Cas had come back before, so maybe… God, please, let it be…

"Cas?" Dean called out.

The man kept walking, and Dean's breathing hitched.

"Cas!"

The figure finally slowed and turned around…and oh god, it was him.

Cas furrowed his brow at them. "Do I know you?"

And just like that, Dean's world came crashing down around him all over again. He pulled up short and reeled back. What kind of sick joke was this?

"Cas?" he asked again, voice cracking with desperation.

Cas's mouth turned down further, and he squinted in confusion before saying with almost tentative hopefulness, "Do you know me?"

Dean's heart dropped into his stomach. No…no, this couldn't be happening.

"Um…" Sam fumbled as he gaped at Cas. "You- you don't recognize us?"

Cas shook his head. "No, I'm sorry. But please don't be offended. I don't know who I am, either."

Dean couldn't believe it. This was just like Emmanuel all over again. Cas had come back from the dead, only with no memory.

But he's alive and he's here, his brain pointed out. And Cas had eventually gotten his memory back that other time.

Dean cleared the thickness in his throat and took a cautious step forward. "Your name is Castiel. Cas for short. I'm Dean, and that's my brother Sam. We're your fr- we're your family."

Cas regarded him a tad warily, like he was torn between being guarded or relieved. It kept Dean from pulling him into the hug he so desperately wanted.

"What's the last thing you remember?" Sam asked.

"I woke up in a field a few days ago. There was no one around, so I started walking, and I haven't stopped since." Cas's face scrunched up in concentration. "I keep having this feeling that I'm supposed to be somewhere, but I don't know where that is. So I just keep walking." He paused, casting them an uncertain look again. "It's strange," Cas added hesitantly. "I don't seem to get tired, or hungry."

His mouth pursed into a thin line, and he flicked a questioning glance between them.

Dean let out a breath of relief. That at least seemed to confirm that Cas was still an angel. Even if he didn't remember he was one.

"You're…not exactly from around here," Dean told him cryptically. "Why don't we take you home and me and Sam will answer all your questions, alright?"

Cas shifted his weight almost nervously, but said, "Alright."

Dean smiled finally, and allowed himself to reach out to at least clasp Cas's shoulder for a brief moment, before turning to head back to the car.

Sam shot him a tense look over Cas's head, but didn't say anything out loud. Dean could understand his brother's trepidation—since when did someone miraculously coming back from the dead with no explanation not have any consequences attached to it? But Dean couldn't care less about any of that, and as far as he was concerned, amnesia was a pretty damn big consequence. But they would find a way to work it out. The most important thing was Cas had come back.

And if there was ever a win Dean needed, this was it.

Sam followed his brother and newly resurrected best friend out of the alley and across the street to the gas station. It was a miracle the Impala was just where they'd left her, gas nozzle in the side panel. Sam almost couldn't believe Dean had dropped everything to run after a sighting of Cas like that—well, he could, and he had, too. Sam had almost been too shocked to speak when they'd caught up to the angel in the alley, only to discover Cas didn't know who they were. Or who he was.

Part of Sam wanted to be suspect of this miraculous event, wondered if they should test Cas for being a shapeshifter or Leviathan, or who the hell knew what else that might have stolen his face.

But even after a few moments, Sam could tell it was really him, just like he'd known when Dean had gotten back from Purgatory. And now Sam felt a conflicting mixture of awed relief and gratitude, but also gut-clenching worry and trepidation. Cas had no memory. Was it the shock of coming back from the dead, or a hard reset? Was it temporary or permanent?

Dean didn't seem to be worried about that so much, or at least wasn't showing it. He quickly put the gas hose back in its cradle and secured the gas cap for the car.

Cas had followed them willingly, but now he stopped and gave the Impala an uncertain look.

Sam jerked into motion and opened the back door for him. Cas gave him a hesitant smile before climbing in, and Sam exchanged a brief look with Dean over the roof of the car. How were they going to explain everything? How would Cas even take it?

Dean slid in behind the wheel, and Sam slipped into the passenger seat as he started up the engine. Then they were pulling out onto the road and heading toward Lebanon.

"So," Cas said after a moment. "Castiel…is an odd name."

Dean chuckled. "Not really. Not for an angel."

Cas didn't respond for a moment. "Um…"

Sam craned his head around. "You're an angel."

Cas quirked a brow at him. "I'm sorry, is that a flirtation?"

Dean choked on a laugh. "No. We mean you're an actual angel, from Heaven. You know, wings, harp. Or, sorry, not the harp. But that's why you don't sleep or eat."

Sam held back a grimace, and studied Cas's reaction carefully. Obviously, he'd already suspected something was…unique about him.

Cas's gaze had seemed to turn inward, like he sometimes used to do when he was using his angel senses. Sam thought he heard a faint rustle in the backseat.

Cas's face screwed up with a wince. "I hadn't noticed them before. Maybe I disconnected from having to feel them? They're broken."

Dean twisted around. "What?"

Cas rolled a shoulder, still squinting in concentration. "There appears to be a lot of old wounds. 'Wings' seems like a gross overstatement. I don't like them. I'm going to try to disconnect them again."

Dean threw a tense look at Sam, but he didn't have anything to say in response. How were they supposed to explain how Cas had lost his wings?

Sam swallowed hard after a few moments. "Are you okay now? They- they don't hurt anymore?"

Had they been hurting Cas the entire time since the angels fell four years ago? Sam had never thought to ask.

"Not as much," Cas replied. "It's a distant pain." He narrowed his eyes at him and Dean suddenly. "You two aren't angels."

Dean shook his head. "Nope, just two regular humans. Hunters, actually. As in we hunt monsters, demons. So do you."

"You said we were family." And there was a hint of doubt and accusation in his tone.

Sam saw the flash of devastation cross his brother's face for a split second, but then Dean cleared it and lifted his gaze to meet Cas's in the rearview mirror.

"We are. We've been through a lot together. An Apocalypse—or three—Hell, Purgatory, gone up against the Devil himself more times than I care to count. And you've been with us through everything. You're as much a brother to me as Sam is."

Cas's expression was pinched as he seemed to be trying to process that. And, really, did Dean have to throw all that out in one go? It was a lot for anyone to take in.

"We've known each other for nine years," Sam said in order to provide some context. "And in the last four, you've spent more time on Earth, helping people, helping us. You like hanging around with us and we like having you."

That was still vague, but Sam didn't know how to explain everything they'd been through together, particularly the bad stuff. Not right now.

"We have become family," Sam went on, flashing back to the moment in that barn when Cas had poured out his heart to them, when he'd come so close to dying. That and the fact that they had lost him later made Sam's eyes prick with moisture. "You- you have no idea how glad we are to see you right now."

Cas was quiet, and then, softly, "What happened to me? Why can't I remember anything?"

Sam exchanged a pained look with Dean, throat constricting further. He turned around to face the backseat.

"Um," he started, knowing he had to be truthful about this, but not wanting to upset Cas, who had to be in an emotionally precarious situation as it was. "Lucifer had gotten free again. He'd fathered a nephilim and wanted to get his hands on the kid, but you'd promised the mother that you would protect the baby. You didn't believe he was evil." Sam swallowed hard. "And you did protect him. You gave your life to keep him safe. Lucifer ended up banished to another dimension where he can't reach us anymore."

Sam flicked a grief-stricken look at his brother, but they both were silent after that. Cas didn't need to know about their mom.

"So, I was dead?" Cas said quietly.

"Yeah," Sam replied.

"Then how am I back?"

Dean shook his head. "I have no idea. But you know what? I don't care. You're back, and that's all that matters."

Cas looked away, out the window at the dark vista. "Am I back, though? I can't remember anything, so I'm not really your friend, not the one you know."

"Well, this ain't exactly the first time you've come back from the dead with a touch of amnesia," Dean said. "Give it some time, and I bet it'll come back to you."

Cas frowned. "I do that a lot? Coming back from the dead?"

Dean snorted. "To be fair, we all kinda do."

"And I've lost my memory before?" Cas continued. "So…so it should come back?" He sounded so hopeful, like he automatically believed Dean at his word.

Dean's throat bobbed. "Yeah. And if not…we'll figure it out."

Sam's heart clenched. Not even twelve hours ago, Dean had given up—on fighting, on believing. And now that Cas was back, Sam's stalwart brother with his indomitable stubbornness was back, too. It didn't matter that things weren't perfect—when were they ever? But just having Cas alive, even if he wasn't whole at the moment, was apparently the thing Dean needed to find his faith again.

And it was enough to help Sam put aside his own worries and doubts, and be thankful that their best friend wasn't lost to them forever.

So maybe Mom wasn't, either.

Cas stared at his lap. "What happened to the child?" he asked after a moment.

"His name is Jack," Sam said with a genuine smile. "And he's doing great. He's, uh, kinda full grown already. Even though he's technically only a few months old. He'll be really happy to see you." Sam almost told Cas that Jack thought of Castiel as his father, but figured that might be a bit too much pressure on the guy, considering he hadn't remembered promising Kelly he'd protect her child with his life, and thus how they'd ended up here.

"Actually," Sam continued, "I'm wondering if he might have been the one to bring you back."

Dean arched a brow at his brother. "Really?"

"We don't know the full extent of his powers. You have any other theories?"

Dean shrugged, and turned his attention back to the road.

The car fell silent after that. Cas had a lot to process, and Sam and Dean would give him time to do so. And from there, well, they'd just have to hope that miracles could come in threes.