Yeah, I'm gonna start a fourth Thor WIP. What could possibly go wrong?

Loki sat bolt upright, his heart pounding and breath coming in gasps. He spent the next few minutes with his arms around his knees, choking back sobs and shivering even though he still had his blankets around him. He hadn't had the dream in years, and he'd started to hope it was gone for good. Nothing really happened in it, and he didn't know why it was so frightening. It was always the same. He was in a vast, dark chamber. It was freezing cold, and he was alone. No matter how loudly he yelled, no one ever came.

He hated that it was back. He was a growing boy of 200. In the last decade, he'd even grown taller than Thor! He was too old for silly nightmares like that. Perhaps it had just come back this one time because of what Father had shown them in the Vault. Yes, that had to be it. Learning about the Frost Giants, seeing their prized Casket, and imagining Father fighting them on their frozen realm had simply reminded his subconscious of it. It didn't make him a coward or a baby.

...But he was alone right now in his chambers, where it was dark and the fire had burned down.

He could have stoked the flames with seidr, but instead he slid out of bed and tiptoed over to his door. He listened hard for a few seconds, then poked his head out. There weren't any servants or guards in the corridor, so he hurried as quietly as possible to the next door over and slipped inside. Thor was sprawled across his bed on his stomach, his mouth open wide. Loki made a face at the sight of the small patch of drool soaking the pillow, but prodded Thor's shoulder. "Brother, wake up!" he whispered urgently. It took several more seconds of increasingly insistent prodding before Thor's face scrunched up and he opened his eyes.

"Loki, what are you doing? I was sleeping!"

"How can you sleep at a time like this? There are Frost Giants attacking Asgard. We're the realm's only hope! Come on!"

A grin spread over Thor's face and all traces of sleepiness vanished in an instant. He gathered his crimson blanket around his shoulders like a cape and tied it off, then stood up on the mattress, fists on hips. With his hair sticking up on one side and the wrinkles of his pillowcase imprinted into his cheek, he didn't exactly look the fearsome warrior, but he believed he did, and that was good enough. "Where are they attacking? They will learn to fear the mighty Thor!"

Loki scowled at him, arms crossed.

"...And Loki, the greatest sorcerer of Asgard!" Thor added hastily. Loki grinned and uncrossed his arms. Good. Thor hadn't forgotten about the snake incident yet.

"They are trying to retrieve the Casket from the Vault so that they can turn all of Asgard to ice!" said Loki. "We must stop them."

Thor blinked and suddenly looked a bit nervous. Loki's imagination usually led the way in their adventures, particularly when they were supposed to be asleep, but he'd never taken them somewhere so out-of-bounds as the Vault.

"...A-are you certain they aren't attacking the kitchens?" said Thor. His stomach chimed in with a low rumble.

"Yes!" said Loki. "They'll get in if we don't stop them! Are you going to let Asgard fall?"

It was Thor's turn to scowl, and he jumped down from the bed. "Of course not! I will defend Asgard to the last." He grabbed a wooden practice sword off the floor where he hadn't bothered to put it away earlier and brandished it fiercely.

Pleased with his work, Loki now followed Thor out into the corridor. He'd figured it all out. If tales of the war and seeing the Casket up close had brought back the dream, then maybe he could chase it away for good if he saw it again and they made up a few tales of their own.

"How are we going to get past the Vault guards?" said Thor as they made a quick stop back in Loki's chambers so that he could retrieve a blanket cape for himself and a pair of practice daggers. (Mother had confiscated all his real ones after the snake incident and he would not get them back for several more weeks, even though Thor was already perfectly well—there wasn't even a scar!)

"I have an idea," said Loki, tying off his green blanket the same way Thor had. "But we can't do it until we're close. I don't think I can hold it very long."

They made their way down the many levels from the royal apartments to the sub-levels, the very bottom of which was the Vault. They had a couple of narrow misses with guards, but they'd done this kind of nightly sneaking about often enough to be quite good at avoiding detection. When they were just around the corner from the corridor with the pair of elaborate gilt doors, Loki grabbed Thor by his cape to stop him rushing farther ahead. "Alright, bend down. I need to climb up on your shoulders."

"What for?" said Thor, frowning.

"The only person the guards will let into the Vault without question is Father. I can make us look like him, but only if we're tall enough."

"Why do I have to be on the bottom?" said Thor crossly.

"Because you're stronger than I am," said Loki, "and I need to concentrate if the illusion is going to hold, which I can't do while walking and carrying you." He probably could have, actually, but Thor didn't need to know that.

"Alright," said Thor with a drawn-out groan. He stuck his practice sword through his belt and crouched down so that Loki could clamber up. The end result felt a bit wobbly—Thor didn't have a great deal of shoulder on which to sit, after all, but they were stable enough as long as Thor kept hold of Loki's knees.

"Good," said Loki. "Here we go." He fixed an image of Father in his mind and concentrated on it as hard as he could, then harnessed some of the tingling seidr that always flowed beneath his skin and formed it into that image. In this position, their total height was rather greater than Odin's, but a bit of extra height was easier to mask than an entire separate person off to the side. From their position, it was difficult to tell whether it had worked, but their reflection in the golden walls was just distinct enough to show them one gray-bearded man in richly embroidered robes where two boys should have been. "Start walking," said Loki. "Make sure to take confident strides just like Father. Any hesitation would seem out of character. But don't say anything, or you'll ruin it."

Thor nodded and walked forward, and in the wall next to them, the dim reflection of Odin also began walking. The two guards flanking the doors stood up straighter as they approached. After the briefest glance at them, their faces snapped to the front. Loki made the illusion give a regal nod, and the guards obligingly opened the doors for their king. Thor walked them through, and the doors closed behind them. Loki waited a few seconds before releasing his seidr, just in case, but the doors remained closed.

"Ha!" he said in triumph, hopping down from Thor's shoulders. "We did it!"

Thor beamed at him. "That was brilliant, Loki! We could go anywhere on Asgard with that trick!"

"Not anywhere," said Loki. "At least not until I work out how to imitate Father's voice as well."

"Well, now we're here," said Thor, drawing his sword again. He looked all around the Vault, free hand on his chin and brow furrowed. "We'll have to check the whole place for weak points if we are to defend it."

"Even if there were cracks in the walls, how do you expect Frost Giants to fit through them?" said Loki. "What we really must do is check for signs of magical intrusion."

Thor frowned. "Fine, you do that. I'm going to check for weak points."

"Just don't touch any of the artifacts!" Loki warned. Thor stuck out his tongue at him and went stomping off, poking his practice sword into corners around the plinths where each artifact sat. Loki left him to it. He raised his hands and made them glow green-gold with his seidr. Magic of the kind he had just described to Thor was far more advanced than what he could do now, but he could at least produce a few effects to make it seem like he was doing it. And he could sense the power of several of the artifacts.

The Warlock's Eye seemed to follow him wherever he went, which was incredibly creepy. The Tuning Fork had an eerie resonance to it that made Loki hurry past it, rubbing his exposed forearms, the hairs of which were standing on end. He spent a little longer in front of the Tablet of Life and Time. Father hadn't said much about that one, but it bore the runic inscription Those Who Sit Above in Shadow. Could it really have been made by the same beings who had made the Aesir, the Vanir, and the Jotnar?

"All secure," said Thor, strutting back to Loki. "Did you find where they'll be coming through?"

Loki feigned a look of extreme effort, making his seidr glow brighter. "I don't think I can hold them! Ahhh!" He made a line of gold appear in thin air a few yards in front of them, and then it opened into a shining doorway, through which two illusory Frost Giants appeared. They weren't very big—only a couple heads taller than Father—, and he would have liked to be able to conjure more, but this was already straining his limits, and he needed to keep enough power reserved to get them back out of the Vault.

"For Asgard!" Thor yelled gleefully, swinging his wooden sword at the nearest illusion. The illusions were silent, didn't have very convincing movements, and Loki had no idea how Frost Giants would actually do battle, but from the way Thor attacked them, they might as well have been the real thing. "Brother, you must secure the Casket!" he said. "I'll hold them off!"

Loki did as instructed, a wide grin on his face. He felt light as air. This had definitely been a good idea. What did he have to fear from stories of Jotunheim and a silly old nightmare? He turned to face the Casket. The relic of a defeated race of monsters, proof of Asgard's superiority. Loki's brow furrowed as he gazed at the swirling blue lights within the Casket. It looked like there was a blizzard trapped inside it. He took a step closer, then another. It was like...it was like it was calling out to him.

"Loki, what are you doing?" said Thor. Loki's concentration was all for the Casket now, so the illusions must have dissipated.

"Can't you hear it?" Loki whispered, only a few feet away from it now. He could hear something like music coming from the Casket. It sounded colder than his dream, but somehow it was still beautiful. Like a winter wind shaped into a melody.

"Hear what?" said Thor.

Loki rolled his eyes. Of course Thor couldn't hear it. He might have incredibly powerful seidr of his own, but he'd never been able to use it for anything but lightning and thunder, and he had very little control over it. It was probably partly due to his impatience for any aspect of their education that didn't involve weapons, but even Mother said it would be near impossible to tame that wild storm enough to wield it for other purposes.

"The Casket is singing," said Loki. "It sounds so melancholy."

"Melancholy over the beating the Jotnar took from Father's army," Thor snickered. "Hey, stop that! We're not allowed to touch the relics. You said so yourself! Father will find out we were down here!"

Loki was barely listening to him. His hand had drifted up towards the Casket. All he could think was that maybe if he got close enough, he'd be able to understand that strange song. He ignored Thor, and gripped the handles.

X

"Loki!" Thor whined, glancing back at the stairs. The doors were still closed, and there was no sound of approaching footsteps, but that could change any moment. Despite his initial misgivings, it had been quite thrilling to get past the guards and sneak into the Vault, but they were certain to get caught if they stayed much longer. Who knew how long Father would have them mucking out the stables and barred from their favorite places and activities for this?

When he turned back around, Loki was still holding onto the Casket, but something was wrong. Thor shivered and tugged his blanket cape around his arms. The Vault was getting colder. The light from the Casket was getting stronger too—Loki was completely bathed in blue light. In a few more seconds, Thor could see his own breath misting in the air. "Loki, let go of that thing! It's turning this place into an ice box!"

Loki still didn't move, and Thor didn't know whether to be scared or angry. Either Loki was in trouble or he was playing a trick on him. Whichever it was, they'd been here far too long, and Loki could stab him as much as he liked, but that wouldn't stop him from carrying him all the way back to the royal apartments if he had to. He ran over and made a grab for Loki's bare forearm, intending to do just that. He had a split-second to notice that what he'd thought was blue light wasn't doing anything to his own skin before he made contact, and then he was recoiling with a yelp of pain. The palm of his hand had turned black, and it felt like it was on fire. Tears welled in his eyes, which he turned reproachfully on his brother. The brief physical contact finally seemed to have distracted him from the Casket, for he released it and turned to face Thor.

Thor yelled and leapt back, pointing wildly at Loki's face with his uninjured hand. Except for the part that he was still the size of an Aesir child and was wearing his same clothes, his brother looked exactly like a Frost Giant. "Stop that right now, Loki! I'm done playing this game! We never should've come down here!"

"What are you talking about?" said Loki. It was bizarre to see that annoyed scowl he knew so well distorted by the lined, blue skin and the fearsome scarlet eyes. "I'm not doing anything."

"What do you call that?" said Thor, pointing even more forcefully. "And this?" He held up his injured hand. "You burned me! Is that what you're going to do whenever Mother confiscates your daggers now? Because if it is, I'm going to figure out how to zap you with lightning the next time you try it, and then you'll be sorry!"

"I—what?" said Loki. He stared at Thor's blackened palm in bewilderment, then raised his own hands. His eyes went wide. "What is this?"

"Don't pretend you're not doing it on purpose!" said Thor. His hand still hurt very badly—much worse than last month's stab wound, and he was struggling to hold back more tears. Warriors weren't supposed to cry, but it hurt!

"But I'm not!" said Loki, and he actually sounded rather panicked as he felt the lines on his face. "Is it—is it all over me?"

"Yes," said Thor, his anger slipping a little in the face of Loki's distress. "Why'd you have to touch the Casket? Now it's cursed you to look like a Frost Giant!"

"You touch it, then!" said Loki. "See if the same thing happens to you."

"I'm not doing that!" Thor protested. "Why would I get myself cursed on purpose?"

Loki seemed to realize that it was a stupid idea even as Thor asked this question. "I didn't mean to hurt you," he said. "I promise. I don't even know how it happened."

"It was when I touched your arm," said Thor, now clenching his other fist in an effort not to show signs of pain. It wasn't just that he wanted to be tough like a Valkyrie or one of the Einherjar now; if Loki really hadn't done it on purpose, then he didn't want to make him feel worse.

"I'm sorry," said Loki, twisting his blue hands together.

"Don't worry about me," said Thor, stepping closer. The air around them was still rather chilly, but it had warmed up considerably in the moments since Loki had released the Casket. What are we going to do about you? How do you break a Frost Giant curse?"

"I don't know," said Loki.

"Is it hurting you at all?"

"No." Loki spread his arms and looked down at himself. "It feels different, but not bad." He squinted his eyelids as though he was standing in direct sunlight. "Everything looks a lot brighter, though."

"Well maybe it'll go away on its own," said Thor hopefully. "Can you do that illusion of Father again so we can get out of here?"

"Not if I can't touch you without giving you frostbite," said Loki, biting his lip.

"We've got these blankets," said Thor, tugging at a corner of his own. "Maybe they'll be enough of a barrier to get us past that corridor."

"As long as you're sure you want to try it," said Loki.

They were able to manage it without too much difficulty. Thor re-tied his own blanket so that it covered his head as well as his back, and then put Loki's blanket on over his front. It probably looked very stupid, but when Loki climbed back up onto his shoulders, none of the bare skin of his arms or legs came in direct contact with Thor. Even though it only took a few seconds for the cold to seep through, it wasn't enough to be painful. Loki cast the illusion over them again and Thor pushed the door open.

Half an hour later, they were slipping back into Loki's room, which was lit only by the wide stripe of moonlight shining in through the window. They both relaxed a little upon getting inside. Even if Mother and Father found out what they'd done, they would at least have until morning before they had to face the consequences of their actions.

Loki walked to the standing mirror next to his bath chamber. "I look like a monster," he said in a small voice.

Thor frowned, joining his brother before the mirror. Loki seemed much more upset now than he had been so far. Maybe he'd been hoping he would be back to normal by the time they got back. Under ordinary circumstances, this would have been a moment to drag Loki into a crushing hug, but that wasn't an option right now, so instead, he hoisted a jovial grin onto his face and thumped Loki on the back. "Don't be daft, Loki! No monster is this small and skinny."

"I'm not the one who's daft," Loki grumbled. "Thor...what if the curse doesn't go away on its own? What if it gets worse? Or...or what if someone else sees me like this and they don't recognize me? What if they throw me in the dungeon or attack me?"

None of those possibilities had occurred to Thor. The idea that he might be stuck looking like this was a horrible one. "If it's not gone in the morning, we'll tell Mother," he said. "She'll know what to do."

Loki nodded. He was fidgeting with his hands again. "Will you—will you stay here tonight?"

Thor would have preferred to go back to his own chambers where he could cradle his burned hand and groan without an audience, but this was the first time in what must have been years that Loki had admitted to being frightened—he'd grown much too keen to prove that he wasn't just the 'baby' brother for that, particularly since passing Thor up in height—and it went directly against Thor's instincts to abandon him when he was specifically asking for his help.

"Please?" Loki added. His bottom lip, still blue like the rest of him, was quivering, and his red eyes were bright with tears that threatened to spill out.

"Oh, alright," said Thor.

Loki smiled, looking enormously relieved. Thor smiled back, and they climbed into the bed and pulled the covers up to their chests. It had only been a few decades since they'd stopped sneaking into each other's rooms and sharing a bed, but Thor well remembered waking up to the feeling of small, ice-cold feet pressed against his bare calf under the blankets. "Make sure you keep your freezing toes to your side of the bed."

Loki giggled, which made Thor feel a little less worried. If he could still laugh, then the curse couldn't be so bad, could it? Maybe it really would go away on its own. Maybe his hand would heal too, and then Mother and Father would never have to find out about their little misadventure in the Vault.

A few minutes passed in silence.

"Loki?"

"What?"

"If you still look like this in the morning, and anyone tries to attack you, they'll have to go through me."

There was a soft rustling sound, and then a blanket-covered hand landed on Thor's and squeezed. Thor squeezed back.

So apparently two fics where Loki finds out his origins under better circumstances aren't enough for my muse. I've wanted to write one set when Thor and Loki were kids for a while, but I couldn't think of a good plot catalyst. I'm of the school of AUs where you can't change the choices the characters make (because that makes them into different characters), you only change some seemingly insignificant detail about the circumstances and let things snowball from there. But then the solution hit me: just give Loki a nightmare he (probably) didn't have in canon! I really like the idea that Loki had a recurring nightmare that he didn't realize was actually a memory of the time he spent abandoned in that temple before Odin found him. That period seems to have informed a great deal about his character.

I cannot tell you how delighted I was to have an opportunity to write the Two Kids in a Trench Coat trope. Even if the trench coat was made of magic and the ruse actually succeeded. CUTIES!

So my idea about Loki and the Casket of Ancient Winters is that he's more susceptible to its influence as a child, which is why he can hear its music and is so mesmerized by it, and also why its effects on his appearance are lasting longer.

I love, love, love writing Thor and Loki as kids. They still squabble plenty and act like idiots as adults, but it's extra adorable when they're little. Also, according to me, Aesir (and Jotnar) take a few centuries to grow to adulthood. Toddlerhood only lasts a few years, and then it starts stretching out dramatically from there. It would just be so sad if they lived for 5000 years and only got to be kids for 12 of them. Besides, they act too much like dumb 20-somethings for me to believe they've already lived many centuries as adults.

This probably will have at least one more chapter, but I don't think it's going to end up being huge.

Please let me know what you thought! Feedback is life!