A/N: Had to pull myself away from this chapter. My OCD has been flaring up lately; still not happy with it, but you guys have waited long enough.

Anyways. This is the final chapter of The Devil You Know, which will be continued in the upcoming story Mortality (also the name of the series as a whole). You guys have been beyond amazing, and I wanted to thank you again for every page view, review, follow, fave, recommendation, and every other flavor of support any of you have given me. The fact that you're still here speaks volumes. You guys are the reason I write, and I LOVE YOU ALL. HUGS ALL AROUND.

So this one-shot turned out kinda angsty. And long. Long and angsty. Like Loki's life. I'd say I'm sorry, but I'm not.

Priorities

The ceiling was hardly exciting even in daylight, but Loki stared up at it now, as he did many nights, watching as the glow of the city cast hard-edged shadows across its surface. The shadows moved from one corner of the ceiling to the other as Loki thought about bleak things like the future.

He rolled onto his side to stare at different shadows.

Tony was dead weight next to him, half his face pressed against his pillow, limbs akimbo and claiming most of the bed. He was sleeping soundly for once, brow uncreased with the stress of nightmares, and though his breath smelled sour, it was from sleep rather than alcohol.

Loki should leave him be, should be grateful that Tony was getting a healthy amount of sleep for once, but he was tired and bored. He shifted so that he 'accidentally' prodded Tony's ribs with his knee, prodded again harder when Tony merely snuffled in his sleep.

The brown eye not pressed into the pillow slit open and blinked blearily at Loki. Loki smiled back softly, apologetically, as though he hadn't just kneed Tony in the ribs.

Tony slurred out something that might have been, "Why are you awake?"

Loki shrugged and murmured, "Can't shut my brain off."

Tony "Mmm'd" and rolled to face Loki fully, one arm snaking about Loki's waist to pull him close and to hold him like a teddy bear.

"Your breath smells," Loki groused, and Tony chuckled and kissed Loki in reply (or retaliation), making the god screw up his face.

"And you take up half the bed."

Tony smiled indulgently. "Mhmm."

"And you drool in your sleep."

Tony arched an eyebrow at Loki, still smiling. And then Loki's hand was on Tony's cheek, soft palm to harsh stubble, and Loki was thinking about how little that actually mattered because one day that side of the bed would be empty and he would miss all the stupid little things that drove him crazy tonight.

"Stop thinking," Tony said, pulling Loki closer to him. And as Loki found himself surrounded by Tony's scent and warmth, he decided that this was the best advice he'd gotten in a while. He closed his eyes.

Loki thought of that night as he stared at the wall, white and stark and no more exciting than the ceiling cut with shadows like the facets of a diamond. He wished he could remember what Tony had smelled like, but the sharp, sterile smell of the hospital was all he could focus on.

'One day' had come sooner than even a god could predict, and Loki felt the faintest tremor in his fingers as they tapped out a rhythm against his thigh.

"I hate you," Loki said to the one other person in the room. The words were thick, spit out like venom.

Thor stopped his pacing, eyes wide and wild like a caged lion's. Loki looked at him with ice in his eyes, swallowing what felt like shards of glass.

"How could you let this happen?" Loki shrieked, and then he was striking Thor - knuckles to jaw, bone to bone - through the sting of tears. Then his arms were pinned to his chest and sides, and the blur of muscle in front of him smelled like sweat and leather and Thor, smelled like home and family. Loki struggled weakly and cursed as tears curved down his cheeks, but Thor held him tightly, mercilessly, and hushed him, susurrating in Asgardian.

"He's still alive," Thor reminded him, one broad hand now cupping the back of Loki's head, the other rubbing circles along his back, and Loki pounded his fist against Thor's chest once more out of spite. Thor gripped him tighter.

The last time Tony had found himself in a hospital bed with a breathing tube shoved up his nose, Pepper had been sitting beside him, face pale and mascara clumped and running from crying. She'd all but squeezed the life out of him when he'd awakened, greeting him with oaths and hiccupping sobs.

Loki sat beside him this time, and though his face was equally pale, his eyes equally shadowed, he was not weeping or flinging himself into Tony's arms (Tony tried hard to banish the thought of Loki with running mascara). He glared instead, expression tight, with his arms folded across his chest.

He looked pissed.

"'Morning, sunshine," Tony said, summoning up his most disarming smile. Something uncertain flickered through Loki's eyes, but he was still most certainly glaring.

"I would slap you if you didn't look so pathetic," Loki replied, his voice matter-of-fact. Tony tried his best to look sheepish. He knew not to take it personally, since he knew Loki must have been sitting by his bedside through the night.

The beat of the heart monitor was slow, mechanical and harsh. The sheets were stiff and scratchy under his hands, stark creases dividing the white fabric into rectangular sections. He tried to smooth them out with his hand, only to stare and blink at the creases in his skin, which was spotted and – and wrinkly.

Tony blinked and swallowed, but Loki distracted him by saying, "I suppose I should ask you how you're feeling."

"I suppose so," Tony said with humor he wasn't feeling. His mind reeled as he stared at his hand, trying to remember if any House episodes had dealt with weird cases like this (that was the extent of his medical knowledge). The rate of the heart monitor picked up minutely. "What happened?" he asked, pulling his gaze away.

Loki was watching him in a way that made Tony feel naked and not in the fun way. The glare was replaced by something more searching, almost concerned. "What do you remember?" Loki asked softly.

"The tomb," Tony answered, brow furrowing. "Lots of old stuff, a few traps. Very Indiana Jones, by the way."

Loki did not smile, and Tony's forced grin slid. He cleared his throat awkwardly.

"I accidentally set off a trap." He shrugged.

Loki's lips thinned. "The trap was cursed," he said quietly.

Tony shrugged again, the gesture more exaggerated. "Yeah, well, I'm okay, right? No harm done?" He determinedly kept his stare on Loki to keep from staring at his hand again.

Tony knew that had been too much to hope for, and his heart sank at the grimace Loki's face twisted into. Tony could see him swallow and knew he wasn't going to like this.

"Tony," Loki said, leaning forward and over the bed. The chair creaked as he shifted. "The curse aged you 50 years."

Steve approached hesitantly, hands in his pockets, as Loki walked back out into the hallway, the door clicking softly shut behind him. Loki's cheekbones stood out harshly against the hollowness of his cheeks, of his eyes.

"How is he?" Steve asked, voice and eyes soft with sympathy. It was all a weird sort of irony, really – here was Steve, young and vital when he should be ancient or dead, and there was Tony, who should be young and spry but – well.

Loki's answering glare hardly came as a surprise. "How do you think he is?" the god snapped, stalking past him.

"Hey, I'm just trying to help!" Steve answered, turning to glare at Loki's retreating back.

Loki wheeled about and marched back up and into his face. "Help?" he growled, teeth grit and eyes so very green this close. Steve took a wary step back, and Loki followed. "Help would have been wonderful while you Neanderthals were off in that tomb. Help would have been spectacular when you or Thor could have taken the lead instead of the one mortal in your little trio. But it's a bit late now, so you can take your 'help' and shove it up your virgin arse!"

Loki turned and stalked back down the hallway, almost visibly fuming, and Steve stared after him, too startled to register anger or humiliation at the god's words.

It turned out that growing old was terrifying. Doubly so when it happened overnight.

Tony wasn't sure whether to laugh or cry when he'd first caught sight of his reflection (correction: when he'd first caught sight of his reflection and realized that it was, in fact, his reflection). Since he wasn't alone, he went with a joking, "Check out that handsome devil."

Steve had sighed but not scolded him. Would wonders never cease.

Pepper – dear, sweet, saintly Pepper – had gotten him set up at home, had fluffed his pillows and brought him food like a good little nurse. But her eyes were always tight, hollow, and too, too soulful when she looked at him, like he was a dog she loved but knew she was going to have to put down soon.

Or a cat, he supposed.

He'd turned to Loki at that thought. The god never seemed to go very far these days. "I miss having a cat to yell at me in the morning, you know," he'd said, lips quirked in a nostalgic smile.

"I'm sorry," Loki had answered, "do I not yell at you enough? I shall strive to do better."

From the weary quality of the words, Tony suspected they may have had this conversation already. He couldn't remember it.

Loki said something else, but Tony couldn't make it out.

Tony could tell that Loki was getting more and more frustrated (they both were) each time he turned his ear towards the god and said, "Eh?" There were times when he just nodded and pretended like he had heard what Loki (or Steve or Pepper or Bruce or Rhodey) had said.

At least Thor's words were always easy to hear.

Tony's eyes followed Loki around the room, settling only when Loki settled, the god sitting at Tony's bedside with yet another heavy book on his knee.

"Loki," he said. He still hated how croaky his voice sounded, how out of breath talking made him.

Loki barely glanced at him before turning back to his book, brow creased in concentration, lines etched deeper and deeper each day. If he didn't know better, Tony would think that he'd been hit with an aging curse as well. "Eat your pudding before I do," Loki said evenly, with a hint of a smile.

Tony's lips pulled up at one corner automatically, but he kept his eyes on Loki. "Loki," he said again. "You know this might be permanent."

Loki's jaw muscles fluttered under the skin, and Loki blinked but did not look at Tony. "The spell will work," Loki said, and Tony could tell that it took effort for him to keep his voice even. Green eyes glared at the book as though hoping to burn a hole through it.

"You said that about the last spell."

Tony swallowed past the tightness in his throat and looked away before the burning in his eyes turned into tears. He didn't want to die just yet and – worse still – he didn't want to live another ten or twenty years like this, shriveled and weak – useless – and the thought of this being his fate eventually, one way or another, made him want to jump off a building sans suit. Tony Stark was a man defined by his youth, doubly so thanks to his eternally-young maybe-boyfriend-lover-thing.

Loki slammed the book shut like a petulant child and turned to stare out the window. In the morning light, Tony could see the faint glimmer of gathering tears in Loki's eyes, could see the tightness of his jaw.

"It will work," Loki grated out through his teeth, throwing a glare over his shoulder. The words it has to were left unsaid, but Tony heard them well enough.

"Loki," Tony said again, and Loki shut his eyes as though pained. "I know you're thinking it. One way or another, today or thirty years from now, this is going to be us. Look at me, please." His voice was gentle, but there was steel in this command. Loki turned back, his green eyes hard, walled off. Tony looked back and smiled softly, sadly. "We were never made to last, and you know that."

Thirty years was nothing to Loki. The fact that Loki was trying so hard to keep him young told Tony clearly how little Loki wanted this, and he didn't blame him, not really.

Loki's stare bored into Tony's, green eyes bright and shrewd and telling him absolutely nothing. "So that's it, is it?" the god said softly, and with his newly terrible hearing, Tony had to lean towards him to make out the words. "Things start to get a little messy, so you want to throw it away?"

Tony's brow furrowed. "What?"

Loki leaned towards him, eyes narrowed threateningly. "I'm not done with you, Tony Stark," he all but growled, "so you can swallow whatever else you were going to say. I'm going to find a way to fix this. Your life is pathetically short enough, and thirty years more is better than nothing until I can –" Loki cut off what he was about to say and licked his lips, turning away.

"I don't want you tied to this," Tony said softly, gazing sadly over his bed-ridden body.

"I already am," Loki snapped, throwing the book to the pile on the floor.

Tony watched him in silence for a long, long moment. Eventually he broke the stillness with a weighted question. "Let's say it is temporary," he said, "or that we fix it, and I age naturally again… what would you do when I got to this point then?"

Loki closed his eyes, wiped a hand over his face. He said nothing.

"I would expect you to leave, you know," Tony said when the silence went on too long. "Or at least want to. I get it. I mean, you're a god, and I'm just –"

"Oh, shut up, you imbecile."

Tony blinked at Loki, who stared down now at his folded hands, eyes open but unseeing.

Slowly, Tony said, "I will if you answer the question."

Loki grimaced, but replied, "Your years are more precious than mine. I'm not about to waste a single one."

Tony sieved through this, more slowly than usual, and in the end he shook his head, uncomprehending. "What are you saying?" he asked.

"I'm saying I'm not leaving you, you bloody fool." Loki shot him another glare, though there was no heart in it. He leaned over Tony and traced a hand down his face as he said, "I don't care if you are old and shriveled or can't even remember how to tie your shoes. So long as even a sliver of you remains, it is mine, do you understand?" There was something dark in Loki's eyes, something unbalanced that made Tony catch his breath, but in the same moment, he understood: there was a threat in there, but above and beyond that, there was a promise.

"Of course," Tony answered, if a bit breathlessly.

Loki nodded, evidently mollified, and sat back.

During the first counter-curse Loki had tried, Tony had watched him with rheumy eyes, holding his wheezy breath, and hoped. It hadn't worked, and Tony had sunk back against the pillows and tried not to look as crushed as he felt. Loki had cursed but assured him there were other spells he could try.

During the second counter-curse, Tony was hopeful, yes, but wary. He was disappointed but unsurprised when it didn't work. Loki had been calm, too calm, with his jaw clenching in a way that Tony knew meant danger. Loki had politely excused himself, and Tony later found out that he'd leveled a copse of trees in Central Park to let off some steam.

During the third counter-curse, Tony sat by politely, waiting for it to fail.

Naturally, that was the spell that took.

Tony hadn't been expecting it, the warmth that flooded his limbs, that shivered down his back and tingled along his skin and settled in the tips of his fingers. He held up his hand, watched the golden glow of healing magic make his skeleton visible through his skin. His bones, muscle, and skin seemed to stretch and pop, and Tony grunted in not-quite-pain as the healing glow pulsed, then ebbed and faded into nothing. Tony's hand, his body, was his again.

Tony let out a shuddering breath, only then aware of the tears gathering in his eyes. He blinked them back and looked up at Loki, who watched him with bright, attentive eyes, the ancient tome of a spellbook still cradled in his spidery fingers.

"Thank you," Tony breathed, half to Loki, half as a prayer to a God he wasn't sure he believed in.

Loki's lips twitched in what could have been the beginnings of a smile, and then he was all business once again, snapping shut the book with a heavy thump and setting it down at the foot of Tony's bed before approaching Tony and examining his hands, his face, tilting his chin every which way and looking into dark eyes.

"How do you feel?" Loki asked, long fingers pausing in their examination of Tony's throat.

"Good as new," Tony answered with a crooked smile.

Then he snared his fingers in long, black hair and pulled the god to him in a victory kiss. Loki made a small noise in protest but allowed himself to be pulled forward, and he kissed back. Those long fingers slid up to cradle the back of Tony's head.

"Now," Tony murmured against Loki's lips, "I really need to stretch my legs."

He winked at Loki before slithering under and by him off the bed, skipping and jumping his way to the door. He shot a goofy smile back at Loki before he rounded the corner and out of sight.

Loki shook his head, smiling softly, exhausted with the weight of his relief.

Apparently, Tony decided that the best way to celebrate his newfound youth was with strangers, loud music, and copious amounts of alcohol. Loki had little use for any of these, though Pepper had handed him a brightly colored drink that she "thought he might like", and he was grateful, if only because it gave his hands something to do.

Loki watched Tony with ancient eyes, watched him laugh and drink and smile, and thought about what was and, worse, what almost had been.

The despair he'd felt had been like falling from the Bifrost all over again.

Loki watched Tony and thought about Idun and her golden apples of eternal youth. He thought that, maybe, the time for wariness and waiting was over.

Tony looked up as Loki took a cautious sip of his mystery drink, and their eyes caught over the sea of faces. Tony's smile turned soft, and Loki echoed it, a thousand thoughts communicated through that one look.

Tony glanced to the side meaningfully, and Loki followed his stare to the empty balcony, cut off from the room's chaos. Tony looked back at Loki, who nodded, and then they both made for the door to the balcony, finally converging in the open air. With the door shut behind them, they were in another world, the sounds of music and voices muffled by the wall even as the bass beat continued to thud in their chests. In the night, the golden glow of the city windows were fallen stars, and Loki searched for shapes among their constellations.

Loki was pulled from his thoughts when his drink was pulled from his hand, and he turned to see Tony sipping at the pale green liquid before making a face and handing the glass back. "Ugh," Tony grunted, still grimacing, "what is that?"

"No idea," Loki answered truthfully, eyes smiling as he took a sip of his own. "But I rather like it."

"Pepper?" Tony asked, arching an eyebrow.

"Pepper," Loki agreed.

Tony sidled up to Loki, cocked his hip against the wall and stared out at the city.

Loki let him have his silence for a long moment before he sighed and asked, "Did you want me out here just so you could taste-test my drink?"

Tony laughed self-deprecatingly and rubbed the back of his neck. "Oh, I have plenty of reasons to want to get you alone," he said with a suggestive eyebrow waggle, "but… well. When you're dying or think you might be dying, it kind of puts things in perspective, you know?"

"I suppose so, yes," Loki replied neutrally. He watched Tony closely, watched him fidget and gesture expansively the way he did when he was uncomfortable. Nothing made Tony more uncomfortable than talking about feelings, so Loki bit back a smile and waited for him to continue.

"What you said," Tony continued, "about staying with me, did you… did you mean that?" His darting gaze finally landed on Loki and stayed there, eyes dark and intense, demanding truth.

Now Loki was the one shifting uncomfortably. "Of course," he answered. His fingers tapped out a rhythm against his glass, and he felt Tony's eyes on him still. He turned to see Tony smiling at him, looking just this side of smug. "It's not polite to stare, you know," Loki groused.

Tony continued to smile and stare, probably well aware that he was making Loki uneasy. "So," he said.

"So…?" Loki prompted into the heavy silence.

"So you plan on staying with me until I die," he said. "Even when I'm old and wrinkly?"

"Especially when you're old and wrinkly," Loki replied with a forced smile. "You'll be too senile to remember all the naughty things I'll do to you."

Tony chuckled softly, gaze finally sliding down. Loki followed the look to see Tony's hand reaching for and then engulfing his own, dark and callused against Loki's long fingers.

"'Til death do us part' and all that, huh?" Tony said, still watching the way their fingers interlaced. Loki looked up, gaze tracing the half-moon curve of Tony's downturned eyelids. "Might as well make it official, don't you think?" Tony's eyes met his again, brightened by a smile but guarded, hopeful, uncertain.

Loki blinked, sieving through these half-insinuations. "Tony Stark," he said at length, eyes narrowing, "are you proposing?"

Tony shrugged, and there was more uncertainty than hope in his eyes now, though the smile was still there, Tony's invisible armor. "Just thought you might make a good trophy wife, you know," he said. "As long as you keep up your figure, anyway."

Loki chuffed and rolled his eyes. "Except I wouldn't be the wife."

"Oh, come on. I'm willing to admit that you would look better in a dress."

"You would look frightful in a dress," Loki agreed, "but that just makes you an ugly wife."

"Ouch. Words can hurt, you know."

Loki shut them both up with a kiss. Maybe even a little tongue. He threw the drink aside, uncaring as glass shattered against cement, and the hand not laced with Tony's laced through Tony's hair instead.

"Alright," Loki answered, "but I'm not wearing the dress."

Tony insisted on telling everyone right then and there. Loki insisted Tony wait until he was sober.

"Then we'll be waiting forever," Tony replied, grip still tight about Loki's hand, tighter still as he used that point of contact to tug Loki along behind him, back through the door into the noise and the party and the press of bodies.

"Engaged" was the word Tony used. It felt odd on Loki's lips as he mouthed it to himself, but that hardly mattered. What mattered was Tony at his side and how Loki planned to keep him there. What mattered was the great smile on Tony's face and the way it would stretch wider and brighter each time it turned to Loki.

Ridiculous, Loki thought but with affection.

At Tony's news, the mass of inebriated strangers gave a celebratory "whoop!", and the Avengers present gaped at the pair in what could have been surprise or horror. Tony beamed drunkenly at the gathered crowd and said, "Now you can start the party!"

As the music boomed back to life, Steve, Natasha, and Clint converged in an isolated corner, hands and arms spread in a universal "wtf?" gesture.

"Am I crazy or will this make Loki heir to everything Tony owns when he dies?" Clint asked, eyes still round. "God, right? He'll outlive Tony and take over everything! We're screwed!"

"This is just drunk-Tony talking, right?" Steve asked. "He'll wake up tomorrow and say he was kidding, right?"

"Should we tell Fury?" Natasha asked.

"I'm not telling Fury," Clint groused.

The trio fell silent when Loki approached them, carrying a tray with glasses of champagne. He handed off the glasses, and the Avengers took the drinks automatically, numbly. "Drink up," he said with a sickly sweet smile. "I suspect you'll need it." He flashed them one more grin, one that said he knew something they didn't, and then vanished into the crowd.

The three watched him for a long moment. Natasha eyed her drink distrustfully, Clint downed his in one gulp, and Steve didn't even bother.

"At least Bruce isn't here to hulk out," Clint pointed out with a shrug. Natasha shook her head and downed her drink too.

But then Steve caught sight of Loki again beyond the press of the crowd. The god stood next to Tony, his back to all the noise and commotion, his eyes and smile soft in a way Steve hadn't seen before.

Steve still hated and distrusted Loki's guts, sure, but that look…

Maybe Thor had been right; maybe Tony brought out something – if not good – at least human in Loki. Maybe there was something there that Steve couldn't see.

Maybe…

Maybe there were worse things, he decided as he watched the two of them. He drank to their health.

Footnote: And that's that. Thanks for reading!