Fathoms Deep

Summary: Tony Stark, renowned genius, playboy, philanthropist, is caught in the clutches of an enemy he thought to be destroyed. He was given an all-too familiar ultimatum: make weapons, or else. Or else what? The answer was simple: they would torture and kill his cellmate. But why should he care about the psychopathic God of Mischief? Post-Avengers, eventual FrostIron. Rated M for language and mature sexual content.

Author's Note: This fic is a monster. I've already finished writing and editing it, so expect an update about every three days. I had way too much fun writing this thing, so I hope you have fun reading it! The title came about because I wrote the majority of this while I was sailing across the Pacific Ocean from California to Hawaii. Inspiration came from reading The Prose Edda, which you really should read if you enjoy Loki and Thor. Get the Jessse Byock translation, so you can know exactly how Loki made Skadi laugh. In my depiction of Loki in this fic, I used a mix of Loki from the Marvel universe as well as from Norse mythology. Also, the translations for the Old Norse I use are in the end notes. I got them from the website "The Vikings of Bjornstad". Without further ado, enjoy!

- Chapter 1: Stone Floors, Stone Walls -

"Are you sure you don't want to call the Avengers, Tony?"

Mechanical arms whirred around him. "Pepper, for the last time, I can handle this." The usual closeness of the suit closed in around his limbs, joints screwed securely in place.

"It has the same readings as the last portal." The helmet closed around Tony's head as Pepper Potts stared up at him, a mixture of annoyance and concern showing plainly on her face.

Tony answered in his usual flippant way. "It's probably just residual from the last one. Besides, I nuked the place. There shouldn't be anything left." The mask clanked down over his face, the screen flickering to life. Automatically, Jarvis ran through the usual diagnostics of the system and the Iron Man suit. Tony looked down at Pepper. Even through the digital image, she looked annoyed. Tony sighed. "If I'm not back by dinner, call the director." Diagnostics complete, he engaged his thrusters and left his assistant-slash-CEO-slash-on-and-off-girlfriend behind, the brightness of the sun bouncing off the tall buildings of New York City taking her place in his field of vision.

The computer butler's voice spoke clearly to Tony. "Should I make that an appointment, sir?"

"No need. Bring up the readings again, Jarvis." Numbers flickered on the screen, steadily rising as he flew closer to the roof of the newly rebuilt Stark Tower. The air above it wavered with energy. "Bingo. Jarvis, calculate the exact wavelength and the counter-wavelength so we can cancel this mess out." The screen flickered as he moved closer to the wavering air.

"Wavelength calculated, sir. Reconfiguring arc energy in the suit."

Tony raised his arms towards the portal energy. "Alright, engage." His repulsors powered up, and the suit went dark. That was not supposed to happen. Tony felt himself fall, and then he was hurtled skyward, though nothing gripped him. In his small view through the eye holes of his mask, he saw only darkness. He was falling… up? If Tony did not know better, he would have assumed that antigravity was taking effect. "Jarvis, give me readings." No matter how he tried, he could not keep the nervousness out of his voice.

"Systems failing, sir."

"Boot the backup," Tony insisted, rapidly moving eyes staring into darkness.

"Backup failed, sir."

"Reboot." He was running out of options.

"I'm afraid I cannot, sir."

"Well, what can you do?"

"Eject."

"Wait- what?" A jolt of fear ran through him. At this rate, he would be too high up in the stratosphere for there to be air to breathe. Then there was the small issue of falling to his death, if he indeed was falling up.

"Ejecting now, sir." Jarvis's voice was as calm as ever.

"No, wait-!"

Before Tony could even flinch, he was hurtled bodily from the suit. Flailing in the darkness, it was all he could do to not yell. Instead, he wrapped his arms about himself, trying to maintain a sense of- a sense of what? Not falling? Nope, he was still falling. Through space, dimensions, who knew what? His journey came to a sudden end when his shoulder struck a hard surface and he rolled to a stop. He finally opened his eyes and was met with more darkness, pure and complete.

"Well, shit." Pressing up on the cold surface, Tony pulled himself to his feet, wincing as a sharp pain shot through his bruised shoulder. "I don't think we're in Kansas anymore, Jarv." There was no response from his butler. In truth, he had not expected one. He turned towards where he thought the suit would have landed when a sudden blinding light stopped him dead in his tracks. When his eyesight cleared, he found himself surrounded by the bioengineered lizard-like creatures that had tried to invade the Earth: the Chitauri.

"Well, shit again. Hey guys, sorry I blew up your-" The blunt end of one of their spears was thrust into his gut, making him double over in the shock of the pain. A bag was thrust over his head and tightened around his neck.

Tony's heart raced, fear sparking red behind his eyes. The last time a bag has been put over his head, he had been a prisoner of war in Afghanistan. No good memories there. He had already had a lifetime of bags over his head. He was bound, hand and foot, all the while struggling for freedom. He was without his suit, feeling vulnerable as a snail without its shell. Pure adrenalin aided his strength, but he was easily overpowered without the added power of the suit. A sharp pain arced through the back of his head and a brilliant, but brief array of stars dashed across his vision.

He woke in a chair, head pounding and limbs bound tight. He opened his eyes, thankful that the bag had been removed. He quickly took in his surroundings, but what he saw brought him little comfort. A chitauri stood before him, just as bug-like and drooling as he remembered. Its sharp tongue made that far too familiar ear-wrenching screech.

Yet another disturbingly familiar voice spoke from just beside him. "He wants you to know his displeasure." The voice was silky smooth, only a vague tendril of distain laced through the words. Tony turned from his captor to see Loki, the freakishly insane, power hungry, kneel-before-me God of Mischief sitting in a chair similar to his own, though he appeared unbound. In that quick sweep, Tony saw that they were both surrounded by fidgeting creatures, each with a mask over its lizard-like face. They hissed jeeringly at them, deathly spears at the ready.

The creature standing just before Tony turned and snarled at the god and spoke in a guttural manner, making a butchery of its English. "Speak no more, teller of lies." Loki's features hardened as he pursed his lips thin, tilting his head back in defiance. It was a motion that made Tony remember just who this person was: a fucking Norse god.

Head still pounding, Tony met his captor's gaze with as much ferocity as he could muster. "Yeah, I'm not sorry for nuking you. Where am I?" His gaze turned to look around the creatures. They appeared to be in a rocky cavern, orange and green lights of a non-Earthly make glowing in the crevices, dimly illuminating his surroundings.

"I ask, you provide, Man of Iron, Destroyer of Worlds." The creature gnashed before him.

"Wow, a title already. I must be more popular than I give myself credit, and I'm not one to hold back crediting myself." The point of a spear was placed on his neck, the metal – or was it stone? – sharp on his flesh. Tony knew when to shut up, and he knew he should have done so much earlier. He was a prisoner, and his life was not in his own hands. He would have to not call the shots in this matter, no matter how it pained him.

"You will be silent." Tony gulped, staring down at the gnarled weapon. The chitauri continued. "You will build us machine like your suit. Can be carried by any. Powered with same device as suit." Well, this sounded disturbingly familiar.

"And if I refuse? Which I'm not at this moment," he added quickly, remembering the last time he had refused. Half drowning in a bucket of water was not the way he had planned to spend his day. "Strictly hypothetical. You'll kill me, right?" He was not expecting these things to be any more merciful than his previous captors in Afghanistan.

The creature grinned, slimy black teeth showing behind thin lips. "We will kill him." The scepter was removed from Tony's neck and pointed at Loki, who met its gaze with his own dagger-like stare. "Torture until you complete."

Tony could have laughed if his life were not hanging in the balance. "Wait, Loki? You obviously don't know who either of us is. He tried to take over my planet, with your help."

"And failed," the creature growled.

"Yes. So, why should I care about the psychotic god?"

The chitauri licked its black lips, the grin returning. "You will."

"I assure you, I won't." Tony looked to the god and saw his face grow stony, not looking at anything in particular. Care about that crazy man? They had to be joking.

"You'll see." With that, the bag was shoved over Tony's head again, making him lurch bodily in terror. Here he was, thinking he had recovered from his post traumatic stress disorder, only to have it all come back in one fell swoop. All of his nightmares of months gone by were coming true and again he felt the cold grip of terror on him.

"You're going to hear from my lawyer!" He called out through clenching fear. Yet another blow to the back of his head turned his world to darkness once again.

Tony woke with a moan, sprawled out on a surprisingly flat and unsurprisingly cold surface. The throbbing of his head had returned with a vengeance. He massaged the back of his head gingerly, glad that he didn't feel any major swelling.

"Greetings, Man of Iron." A cool and collected voice broke through his silent suffering. He looked up to see the god perched on the edge of a singularly grimy and bare raised sleeping pad, peering down his nose at the mortal. He sat so tall and regally that even his casual godly garb looked just as grand as his armor. He was no less intimidating without his armor; no less a god.

"Hello back, oh insane one." Tony, for the second time that day, pressed himself up from the floor and into a sitting position. His whole body ached, though he made sure to show no weakness before his enemy. He did massage his temple with a hand, the headache almost overwhelming. "Didn't think I'd be rooming with you. I could have sworn I'd signed up for a single."

"It was no decision of mine, ósælligr oskilgetinn," the god spat. For some reason, Tony felt he had just been insulted in Old Norse.

Looking past that, he sighed. "I know how I got here, more or less, but what about you? Can't you just teleport your way out? You seem to be able to get around easily enough on Earth." Hell, he'd gotten out of Bruce's magic glass box.

Loki sneered, turning his anger to the surrounding walls that looked rather like concrete, though Tony knew them to be carved out of stone, just like the hard floor he had come to know so well. "These walls prevent me from doing so."

"You are supposed to be in Asgard with Thor."

"Indeed, I was there. Then quite suddenly, I was carted from one prison cell to another." He sounded more annoyed than angry.

"Just jail time for trying to take over my planet and destroying half of New York City?" Damn, he had expected more of Thor. Then again, Loki was his brother, adopted or no.

The god's eyes darkened, staring into himself rather than at Tony. "No imprisonment in Asgard is quite so forgiving. Believe me, if you can, that I have had my fair share of punishments."

The animosity towards the god was no less in Tony's heart. For all their trouble, and the death of their comrade Agent Coulson, Tony felt he would never be satisfied with his punishment. "Oh, I know about Asgardian punishments. After you and your friends - who, by the way, are not the nicest minions – tried to take over my planet, I caught up on your history. Mythology. Whatnot." He leaned forward, gaze trying to penetrate that dull stare. "You bring about the apocalypse, right?"

"Ragnarok, indeed."

A dead silence rang within that rather extensive, cold, cluttered cell. Unable to cope with the silence, Tony spoke up.

"Okay, introductions. The last two times we met, we never officially introduced ourselves."

Finally, those almost glowing green eyes turned on him, as if seeing Tony for the first time. They were cold with anger. "You blasted me into the town square, bacraut."

Yet another insult he could not understand. Tony shrugged. "You threw me out of my window." They stared each other down for an agonizing moment, each waiting to see who would make the first move, whether it would be to attack or talk.

Loki was the one to break the challenge. He sighed. "I am Loki Odinson of Asgard, Laufeyson of Jotunheim, God of Lies and Mischief, Author of Woes, the Sly God, the One who Slanders and Betrays the Gods, the Liesmith, Silvertongue, Master of Sorcery and Shape-shifting. There are… many more titles."

"Tony Stark, genius, playboy, philanthropist." Short, sweet and- wait, shape shifting? He had never seen the god do that. "You can change your shape? Like the Hulk, but without the whole bloodthirsty thing?" At the mention of the Hulk, the god winced ever so slightly.

Loki's voice was sharp. "It is an esteemed craft in Asgard, though it tends to just bring me trouble."

For better or worse, this piece of information piqued Tony's curiosity. He had always been one to venture into the unknown and possibly dangerous. "Pray showeth and tell."

The god's eyes flashed for a moment, though his expression was still as stony as ever. "On one condition."

"Name it," Tony was quick to agree.

"Tell me why I could not use the scepter on you, like I did to your bowman."

"Done. Now, I want to see you outdo the Mighty Morphing Power Rangers."

Loki stood, the long coat he wore falling regally behind him. With outstretched arms and closed eyes, he began to mumble words Tony could not quite pick out, but they were definitely in no language he had ever encountered. In a flash of blinding light, the god disappeared and a beautiful falcon hovered on thin, beating wings.

Tony's awe was cut short by the banging open of the cell door. He jolted to his feet automatically, raising his hands to his head as he turned towards the sound. A chitauri guard rushed by him, quite ignoring him and thrust one of those mean looking scepters deep into the feathered chest of the flapping bird. The point of the weapon cracked with electricity, and suddenly the god was in his original form, hovering mid-air. The scream he gave off as the lightning cracked into his chest pierced though Tony, jolting yet another wave of fear through him. Loki fell to the floor in a boneless heap just beside the bare, rough bed, his shriek replaced with a dull silence.

The chitauri retreated just as fast as it had come, spitting out, "No magic, Odinson," just before the door slammed shut once more on the far side of the room.

When the god did not move for too long a moment, a pang of what felt like the tiniest bit of worry made Tony reach out for the god, though he dared not move from where he stood, arms slowly lowering at his side. "Hey Falcon Punch, you still alive?"

The unmoving heap let out a weak moan. It shifted slightly, followed by a muffled and strained, "I've had worse."

"Really?"

Using the edge of the bed, Loki pulled himself upright, breathing heavy with the effort. All sense of godliness was gone and he simply looked broken. "My brother is the God of Thunder. I may have angered him a time or two. You know how he is."

"Makes sense," Tony replied, watching as the god pressed a palm to his chest, grimacing as he did so. "So, that bird thing. Pretty cool."

"Falcon," Loki growled, "Freyja's Falcon. It's gotten me out of some tough spots. And into some." That last had been muttered bitterly.

"Explain," Tony prodded encouragingly. Loki gripped the mattress and struggled to his feet. Tony moved to aid him, but he stopped his forward movement when he was struck by a glare that said 'no mortal should help a god.' On shaky arms, Loki gingerly lowered himself into his previous sitting position, albeit less regally than before.

Loki sighed, smoothing back his long raven black hair. "I once was looking upon a court in that form. Just for fun. Needless to say, given my luck, I was captured and trapped in a box for three months." Tony reeled internally. That sounded far too familiar. The god seemed to notice that change in his expression, so he continued. "Indeed, Stark. I am no stranger to being held captive. It comes with the title The Slanderer and Betrayer of Gods. Safer to keep me locked up," he added bitterly.

Mostly surprised by Loki's forthcoming with the story and secondary by the punishment for such a seemingly small crime, Tony looked at the god with a new eye. "And here I thought I was the one with the most experience in being practically entombed."

The god's eyes grew distant once more. "No mortal could live through what I've suffered."

Tony shrugged. "Yes, well. You are a god. Three months is hardly a blip for you." It had seemed like an eternity to him.

Loki lowered his head. His voice was as small as he looked. "It is no less lonely." He sat straighter, and spoke stronger. "At least for my longer sentence, my wife was with me. She kept the venom from dripping on my face, for as long as she was able."

"Your wife?" That seemed more shocking than the venom on the face part.

"Estranged," he explained shortly.

Well, there he had it. "Ah. I have plenty of those. Estrangements, I mean."

The god met his prying gaze. "As a genius, playboy, philanthropist, I am sure you do."

Tony forced a grin. "I appreciate that you remembered all that. I would return the favor, but I really don't think I could remember all of your titles. The one who betrays gods and shape-shifts while writing woe. You ever think of making an acronym?"

"Slanders and Betrays," Loki corrected, sounding worn of the subject.

"Quite the reputation, Odinson of godland, Laufeyson of yo-yo-heim… etcetera."

"Just Loki. Please, just call me Loki." He sounded almost as exhausted as he looked.

"Loki," Tony tested the name.

He nodded. "Stark. You have a reputation as well."

"The Man of Iron, as your beloved brother calls it. It has gotten me out of some scrapes, but mostly just in to them. Just like your shape-shifting has, I guess."

"Yes," the god replied softly, the silence trailing on for a long moment. As the conversation appeared to have ended, Tony stepped across the cold floor and began a brief reconnaissance of the room. It did not take long, as the clutter, lit by the same green and orange light as the cavern was, appeared to be just that, junk, sitting atop and around simple tables made of stone and metal. The clutter made the room look like a place where the chitauri dumped their old crap. He kept pacing the room, for lack of anything better to do. Sleep would not come easily, he knew. He began thinking on the problem presented to him.

It was Loki's question that brought him out of his silent brooding. "The Chitauri asked you to do what, exactly?"

Tony instantly leapt into his current thought process. "Delineate the quantum mechanics of my arc reactor's energy so I can use its raw energy in a foreign projectile." He glanced at Loki's blank expression and decided to clarify. "They want me to make guns. Not something I'm unused to.

Loki's brow furrowed with deep thought. "They captured us both so that you could make instruments of war?"

"Seems they didn't destroy enough of New York City when they came to Earth. Now they want to do it again, but with more sparks."

Ignoring Tony, Loki continued his thought. "And I am to be your leverage."

He rolled his eyes. "You are my jail keeper?"

"No," Loki replied slowly, brow deep with thought, hands clasped and pressed to his lips. "They dislike me, especially The Other. I took his army and lead it to destruction. I think this is revenge. They just want you to do as they bid in exchange for not killing me. They win both ways. If you don't make your weapon, they get to kill me and if you do, they get the weapon."

Tony walked to the door and back again to the far wall. "Why should I care about you? You tried to take over my planet, blew up my city, and-"

"Threw you out the window, yes." His words hung heavy in the air, as if he were admitting a grave crime.

"Even after I offered you a drink." The light comment did nothing to lighten the darkness that seemed to seep from the god.

"'You'll see' they said." Back and forth, around the benches, past the various piles of junk, Tony walked, the god growing more and more annoyed with each step. He finally raised his gaze, green eyes dark with annoyance. "Would you stop pacing?"

"I don't do well in boxes." The comment was met only with the continued stare of the god, so Tony continued. "I was trapped in one once, though there were a lot more guns. I came out of it with a car battery attached to my heart. No, I don't like boxes."

The green stare continued. "Your heart needed a source of power?"

Tony finally stood still, his fingers brushing the edge of the arc reactor. He could almost hear his own distant screams ring in his ears; feel the scalpels digging out the shrapnel. He blinked, returning to the current cage he was in. "I don't tell this to many people. Security reasons and all. I guess I do owe you an explanation in exchange for your turning into that falcon." He tapped the reactor. "This arc reactor is what keeps me alive. It powers an electromagnet which is stopping shrapnel from entering my heart. It is also the reason you could not control me with your fancy glowing scepter. A heart of metal cannot be controlled."

The god nodded. "Neither can a heart of mischief." Their gazes met, then. They stared deeply into one another, both searching for something that neither of them showed outright. Tony broke the moment first, turning away to continue his restless pacing.

Loki sighed and lay back on the mattress. "Well," he said tiredly, "you continue your worthless pacing. I am going to rest."

Tony stopped, staring at the god. "What, you hogging the bed?"

Loki gave a flippant gesture. "By all means, sleep on the floor if you wish not to share." Share a crappy mattress with an insane god who tried to kill him? He had to be joking.

Tony stared him down, but found the act was useless as the god had already closed his eyes to the dim light. "I still don't trust you."

"Very wise not to, given what I am. I did intend to take your soul as mine as I did with your colleague, and when I could not, I tried to end you." The god spoke truth.

A hesitant moment, then, "But you didn't."

"Like I said, floor or share. It matters not to me." With that, Loki refused to speak more to Tony. He continued pacing, making a point to step as loudly as he could across the smooth stone floor. He worked out equations in his head as he paced, trying to figure out the best method to modify the arc power into a useable projectile without giving away how his repulsors functioned. It was a problem that he had to work out – or else. Or else what? They would hurt Loki? He really did not care for the god. Did he?

Tony sat on the cold floor, back against one of the stone benches, well away from where the god slept. Staring longingly at the crudely stuffed mattress, he drifted off to sleep just as the orange and green lights dimmed and died.

End Notes: Translation of Loki's Old Norse insults:

Ósælligr oskilgetinn – wretched bastard. Bacraut – Asshole.

Stay tuned for the next chapter!