Disclaimer: I don't own The Avengers, Thor, the various Marvel comics series, or any of the characters therein.

Warning: The fic as a whole contains character death and a slash pairing (specifically Tony/Loki or FrostIron). Also, spoilers for Thor: The Dark World.

Notes: Written as a gift for Enk/enkanowen for FrostIron Fest 2013.

A Serpent's Tooth

For most couples, the revelation that one of the partners had children from a previous relationship would be broached delicately, and any suggestion that the other partner should meet them would be made with all due seriousness. It would perhaps be prefaced by phrases like, "I feel it's time to take our relationship to the next level," or "You're already an important part of my life, and I'd like you to be part of theirs as well."

Of course, as anyone in SHIELD could tell you, Tony Stark and Loki Laufeyson were not exactly a typical couple. And so, the momentous topic was raised in the following way:

"I think you ought to meet my children."

This statement was immediately followed by the sound of Tony choking on his scotch.

"So, explain the plan to me again?"

"I'm going to use the Casket to put both of us in a state of suspended animation, like a much more sophisticated version of your cryogenics. I will then guide our minds to the realm of the dead so that you can meet Hel."

"...Nope, it doesn't sound any better than it did the first time."

"Are you backing out, then?"

"JARVIS, can you explain to our friend how good I am at backing out of really, really bad ideas?"

"On a scale of one to ten, approximately negative thirty-two thousand, sir."

"And there you have it." Tony eased himself onto the couch, leaning back against what felt like a small mountain of pillows.

"Are you ready?" Loki looked over at him from the neighboring couch. He was already holding the Casket of Ancient Winters, and thin tendrils of ice were snaking their way up his arms.

"As ready as I'm ever gonna get, I suspect."

Loki reached up a hand whose fingers were already tinted blue and opened the Casket.

The light that spilled out reminded Tony of some hiking he'd done in Alaska. The sun had reflected off the snow and made it seem as though the ground were covered in diamonds. When Tony had lifted his sunglasses to get an untinted view of his surroundings, he'd been forced to squinch his eyes shut. But despite the dazzling brightness of the light, there was no warmth in it. Tony had been able to feel the cold even through his insulated parka, boots, also-insulated clothing, and the ridiculous thermal underwear Pepper had insisted he bring along. The Casket was the same: it filled the room with a light that was utterly devoid of the warmth that usually made light so comforting.

It didn't hurt, though. That reassured Tony until he remembered that when you were freezing to death, you eventually stopped feeling cold. You just felt really, really tired, so that even a snowdrift started to look as appealing as a featherbed. If you were foolish enough to lie down, you would feel relieved and comfortable...and then you would die.

He reminded himself that he had JARVIS watching over his vital signs. Surely it would be able to tell the difference between freezing-to-death and almost-but-not-quite-freezing-to-death?

It occurred to him to wonder whether using the Casket had caused a full transformation in Loki's appearance. But the light that was still pouring from the Casket was so intense that he couldn't even look in the other man's direction. Besides, the pillows were so soft, and the cold wasn't really so bad once you got used to it...

"So, did it work? Are we all dead, or only mostly dead?" He looked around. "And is this really Hel's realm? It just looks like a foggy plain with a lot of doors to me."

Everything was grey. Grey grass, grey sky, grey doors of every description. There were simple wooden doors with peeling paint, ornate doors of hammered metal embellished with designs of leaves and flowers, open stone arches. The doors were all around them, and the plain stretched away in every direction before fading into a thick fog.

"To answer your first question, yes, it worked. To answer your second, we are in suspended animation, or as you so crudely put it, only mostly dead. And for your third, what did you expect?"

"Well, I don't know, maybe some pearly gates or a big scale with a feather on it or something. I mean, people come here when they die and this is all they get? No greeting, no judgment, just a bunch of doors? How do you even know which one you're supposed to go through?"

Loki rolled his eyes. "Luckily, the universe doesn't share your love of the melodramatic. The doors are metaphors. They represent crossings into other planes of existence. As for how you know where to go...it's the subject of quite a lot of debate, actually. There aren't exactly a multitude of people who've been through the experience and come back to report on it. The general consensus is that you're inexorably drawn to one of the various portals, though the precise mechanism by which this works is unclear. You'll note, however, that we aren't being pulled toward any of them, which is how I knew that the procedure worked."

"And we have a set amount of time before our bodies thaw out, right? So, let's go meet your daughter."

Loki arched an eyebrow. "You already have."

"What?" Tony spun around in a circle. Nope, nothing that looked like an Asgardian. Or a Jotun. Whatever. Just more doors and more fog. "Is she invisible or something? Can you only see her if you're about to die?"

"I most certainly hope not, given that I'm looking at her right now. As are you." Loki gestured at the mist that hung heavy over the landscape, twining sinuously around the doors and arches. "Hel permeates this plane. She's everywhere at once. You've been quite literally walking through her for the past ten minutes."

"Wait. You mean this fog stuff is your daughter?"

Loki nodded.

"I've been inhaling your daughter?"

"...That horse has eight legs."

"Yes, it does."

"Also, it's a horse."

"Yes, it is."

Tony stared at Loki.

"Look, it was one time and I was drunk, okay?"

Having been on both previous cruises of the Stark Industries Experimental Spacecraft for Asteroid Mining, Tony had seen the asteroid belt before. That didn't make him any less awed by the sheer scale of the chunks of rock that floated past them, or by the mysteries that lay hidden under their craggy surfaces. Not just the potential mineral wealth that had sold the Board of Directors on the project, but the possibility of learning more about the birth of the solar system that had given rise to everything from the Lascaux cave paintings to the Iron Man suit.

Glancing over at Loki, Tony was surprised to see a faint smile on the Asgardian's face. "What?"

"You look the way I imagine I looked the first time I saw the Bifrost," he answered. "The realization that the universe is a much bigger place than you had previously thought."

"You still haven't explained to me what we're doing out here."

"We're meeting another of my children," Loki said.

"One of your children lives in the asteroid belt?"

"In a manner of speaking. You said this craft includes a prototype for a dark matter detection device?"

"Yeah, it works by detecting the gravitational distortions that dark matter creates."

"Turn it on."

Tony fiddled with a few knobs and dials. One of the many screens on the walls around them lit up. "Hey, whaddaya know, it works! Whoa. This whole place is full of...dark...wait."

"Yes?" There was still a smile on Loki's face, but it was significantly more mischievous than it had been a second ago.

"Loki?"

"Yes?" he repeated in the same maddeningly curious tone.

"According to the instrumentation, there's a ring of dark matter colocalized with the asteroid belt. It has an exceptionally regular boundary, conforming largely to the elliptical orbit of the various bodies within the belt. And being that it fills the same space as the belt, it's millions of miles in diameter. This is...Loki, this in an unprecedented discovery! Well, for human science anyway," he amended. "That look you're giving me tells me you've known this was here all along."

"Seeing as how I made it, yes, I did. Tony Stark, say hello to Jormungandr."

All of the Avengers and almost every SHIELD agent he'd ever met had, at one time or another, commented on Tony's seemingly pathological inability to stop talking for more than five seconds at a time. But not only had the Norse god's matter-of-fact statement rendered him speechless, it wasn't the first time, or even the tenth, that had happened. That probably deserved some kind of award, or possibly an entry in the Guinness Book of World Records, Tony reflected.

"You...made a ring of dark matter circling half the Solar System? How? No, scratch that, why?"

"As an experiment," Loki said cheerfully. "It is the result of a confluence between two lines of theoretical research: the manipulation of non-conventional forms of matter and energy, and the creation of artificial life-forms."

"Are you saying that this dark matter ring is alive?"

"Jormungandr is very much alive, though he's been asleep for quite some time now. Which is lucky for you; were he awake, these asteroids would be far less stable in position."

A slight tremor went through the ship at that moment, and Tony turned away from Loki's infuriating smirk to scrutinize the instrumentation. "The dark matter ring-er, I mean Jormungandr, I guess-is moving. That vibration we just felt was a gravitational distortion."

"What? Why would that be happening?"

"I don't know. Nothing we've done has actually affected it-him-whatever-in any way; it's all been just passive scans. Do you know what kind of perceptual abilities Jormungandr has? Would he recognize the approach of a space vessel even in his sleep?"

"He shouldn't, not unless that sleep is much lighter than it was designed to be. Then again..."

Another wave rocked the ship, a stronger one this time. "Then again what?"

"Circumstances haven't exactly been normal lately. The Conjunction, the...regrettable incident...with the Chitauri, the reappearance of the Phoenix Force you told me about, those all had effects that resonated beyond Midgard. And those were on a scale that might have penetrated to the deep levels of the subconscious that Jormungandr still has access to while asleep. It may be that one or all of those events began the process of waking him up."

"And by showing up on his doorstep with his creator and the arc reactor powering this ship, we've finished it? Great. So what do we do now?"

Loki didn't answer right away, and Tony was shocked to see a look of naked fear on his face. To most people, Loki seemed unflappable, greeting any setback or unexpected catastrophe with either blithe unconcern or blistering sarcasm. Tony was pretty sure that he and Thor, and maybe Frigga when she was alive, were the only ones who could, on a regular basis, see that mask for what it was. Loki could be uncertain, could be frightened, he just refused to show it. But now he wasn't making even a token attempt to hide the fact that he was absolutely fucking terrified.

"Loki? Talk to me, buddy. What's going on? How do we put your not-so-little bundle of joy back to sleep?"

Loki didn't look at him. His eyes were fixed on a display screen showing the ever-escalating gravitational anomalies. The apparatus had made a rough map of Jormungandr and was tracking its movements in real time. There was a crack appearing in the ring at a point not too distant from them. As Loki and Tony watched the screen, the crack grew wider, splitting the ring completely. Now it wasn't so much a ring as a sinuous, snakelike shape curled around the asteroid belt. The broken ends of the ring were tapering, so that they looked like the head and tail of a gigantic serpent.

Finally, Loki answered Tony's question. "I'm not entirely sure we can. Jormungandr's waking has been prophesied, and it's only the beginning. The beginning of the end, so to speak."

"The end of what?"

"The world."

A/N: The FrostIron Fest prompt I wrote this for was: "Loki introduces Tony to his children (and it is terrifying/hilarious) and accidentally awakens Jormungandr, thus ringing in Ragnarok/the end of times."

When I posted this on AO3, I did it as a single chapter, because I didn't know if the FrostIron Fest collection would allow a single participant to submit more than one document. But I think the fic works better as three separate chapters, so that's how I'll be posting it here.

The title is from Shakespeare: "How sharper than a serpent's tooth it is to have a thankless child."