I don't own the Avengers or Rise of the Guardians. This story takes place after the events of both films and they are referenced so if you haven't seen them (and are still reading this) you might be confused.

1. Puzzle

Tony Stark hummed to himself in approval as he finished making the latest fixes to his tower's security systems. The Stark Tower was still under heavy renovations after the whole mess with the alien invaders and a mad-with-power Norse god that had taken out chunks of Tony's sweet home. Now it had mostly been patched up, but Tony had figured it was only necessary to boost his security while he was at it. Now he was pretty damn sure no one could get in without JARVIS noticing it. If there was something that somehow slipped past JARVIS, it was because it didn't exist. Now that that was taken care of, Tony could focus on other things, like maybe fashioning living floors for all of the Avengers, who seemed to now really form a team just like Fury had wished. Well, at least as much of a team as a group of very different people who were now in very different sides of the planet – and in some cases, not exactly even on the planet – could be.

While the Stark Tower was being fixed, the rest of Manhattan was also under repairs. By now, most of the buildings and streets were at least usable. The window retailers and manufacturers were much richer than before and people in the central buildings could go back to work. What was harder to fix was the people's peace of mind. Facing an alien invasion and almost being nuked usually had a rather harrowing effect on people. These things tended to stay in memory for a long time, even now after all the funerals were over.

Tony turned his attention from JARVIS to his Iron Man armour. He had needed to rebuild the Mark VII suit almost entirely after chucking the nuclear missile to the Chitauri mothership. He had taken care to make some adjustments to the suit's durability, in case he needed to hang out in the vacuum of space more often now that he had discovered the joys of true altruism. His shiny, repaired suit was now standing in front of him, red and golden and begging to be tested one more time. Tony wasn't going to say no to that. He'd spent at least two days cooped up in his penthouse, making his new adjustments for JARVIS.

"JARVIS," Tony said, "I'm going out. I'm taking the suit."

"Very well, sir."

It was a rather nice summer evening outside, if one cared about such things. Tony flew a few rounds over the city centre and noted with satisfaction that the hours he had spent adjusting the suit after the last test flight had paid off; his movement felt much more fluid than before. He sped over Manhattan and plunged towards the water when he got to the bay. He stopped just above the surface and flew higher again, breaking through the aerial currents with ease. Good, everything was working fine. It had been an exceptionally good day for Tony. He would have been more happy about that if he hadn't been so sure that a nice day like that could only be followed by an exceptionally bad one.

He spent some more time in the air, staying above the Atlantic and only heading back towards his tower once it was getting late and New York was only a bunch of blinking lights in the darkness. Tony was halfway back and already planning what type of drink he would have to celebrate such a good testing day when something sent him off course and almost to the wall of a skyscraper. He quickly righted himself and looked around.

"JARVIS? Scan the area."

A few screens appeared into Tony's field of vision, all depicting the area through different filters. To be fair, it didn't do much seeing how even the airspace of Manhattan was always rather crowded and full of all sorts of signals. Tony flew upwards, scanning the sky for anything that might have been hostile. What had hit him hadn't been anything solid. It was more like a shockwave of energy, probably residue from some sort of explosion. Great, wasn't that exactly what the world needed? More explosions.

Tony finally stopped when he was hovering just above his tower. And that was when it happened again. This time it was farther away, and it only swayed him a little. But now he saw it, and he realized he had missed it previously because while it indeed was some sort of energy blast, it was as dark as the night sky and camouflaged into it save for a few flashes of gold among it. Tony frowned at the phenomenon and forgot all about his drink. He directed most of the power in the suit to propel him towards the explosion as fast as possible.

He reached the scene of the dark light quickly, but apparently not quickly enough. Whatever had caused it was nowhere to be seen. The night was silent and there wasn't even any debris from whatever it was that had blown up. If it indeed was something that had blown up.

Tony sighed.
"Well, at least it didn't happen any closer to the city than this."

He still commanded JARVIS to scan the area once more through some filters. All he could detect was some residue energy that he couldn't identify at the moment. He would have wanted to look into it even more, but he didn't exactly have any means of bagging something intangible and unknown for further studies. At least not at the moment.

"Sir," JARVIS derailed his train of thought, "a foreign object is falling towards the ground. Seems to be metallic."

"What? Where?"

JARVIS gave him video feed and readings and Tony was on his way. The object was small and it was falling fast. Damn. Tony had kind of hoped he wouldn't have to stop any more explosives for a while. He sped up and dodged a flagpole on the tip of a building. The falling object clinked softly as it hit the roof of the skyscraper and bounced back up. Tony caught it before it could continue its descent and shot back up into the sky, clutching the object firmly in his hand. Only when he was high enough so that the city was safe did he open his metal-covered hand.

"What the-?"

The object was shiny and cylindrical. It looked harmless enough, with its filigree decorations – which for the record would have been an unbelievable waste of money if the thing had been meant to blow up – and a portrait of a child at the base. But of course, extremely dangerous things could very easily be disguised to look innocent. Tony frowned at the cylinder and dared to shake it just a little. It rattled softly. There was something inside, but Tony didn't see how it could have been opened without damaging it. A puzzle box.

"I really hope this just fell out of a plane or something," Tony said out loud, "Because otherwise this is just weird."

He really wasn't in the mood for facing a mysterious attacker with a very gimmicky weapon. At least not before a good night's sleep. Oh, yes, and the drink he had wanted.

"JARVIS, what do you think?" he asked.

"It seems to be a container, sir," JARVIS said rather unhelpfully, "It doesn't seem to have any electronic functions or anything explosive in it."

What actually was inside the box was harder to say. If Tony wanted to know, he would have to take it to the lab. And boy did he want to know. He sped back into his tower, disturbing a few lonely, brightly coloured feathers that were gently floating towards the nightly streets.

It was on the news the very next morning. Someone had captured poor-quality, grainy footage of the strange phenomenon on the sky. That someone's YouTube -channel had become a hit in about five hours. Tony watched it together with Pepper, who had managed to find time for a quiet moment in the morning even with the exceptionally full schedule she had for the week.

"Experts are looking into this strange phenomenon, but so far there is no definitive answer to what it was caused by."

"So you said you were there?" Pepper asked from where she sat curled up at the corner of a sofa, her long legs draped over the armrest.

Tony nodded and turned the puzzle box in his hands for the nth time that morning. He had examined it late into the night, and it interested him more with every detail he figured out about it. Just because it didn't make any sense to him. And because it was a bit embarrassing that he, Tony Stark, a genius, hadn't been able to open a puzzle box even after hours of trying.

"We are advising people to not panic, as there is no indication that whatever happened has caused any danger."

"It almost knocked me to a building," Tony said absently, "I don't know what it was. Some sort of energy. I couldn't find anything it could have come from."

Pepper swept a loose strand of strawberry blonde hair behind her ear.
"So what do you think it was?"

Tony shrugged.
"I'm going to keep my options open. A lot of weirdness has been happening lately."
He shook the puzzle box.
"I can be pretty sure it's not the Chitauri, at least."

"Well, that's comforting."

"Do you know what's inside this thing?" Tony asked suddenly, holding the decorated cylinder up for Pepper to see.

Pepper frowned.
"No. What?"

"Teeth."

"Not yours," Pepper said matter-of-factly.

"Nope. It fell from the sky. I can't open it yet, but I know there's teeth inside it."

"Well, that's... weird."

"I know," Tony tapped the surface of the box with his finger, "I don't have any meetings today, do I?"

"You are going to spend your day with a box of teeth?" Pepper asked with her brows raised.

Tony smirked at her.
"Well, the day, yes. But as for the night... if you're not too busy?"

Pepper laughed and flashed a smile of her own.

In the background the TV kept going, and the news changed to weather reports.

"The night has been unusually cold, and it has left some of the roads slippery with frost. People at the centre of Manhattan are advised to move with some caution."

Author's Note: Okay, writer's block is gone, so I am now taking a journey. A journey waaaaaaaaay out of my comfort zone. There are so many reasons why this fic can (and probably will) be terrible, and yet I'm trying it. Take cover and save yourselves, or alternatively, help me on this journey by giving me some feedback!

Okay, first of all: Crossover. I've never written one. Second: Avengers. I've seen it and I liked it almost as much as I can like a superhero film. I haven't read any Avengers comics nor have I even seen all of the other films that lead up to the Avengers. I know how they sort of go, but... yeah, I suck. Third: well, those first two were already big ones, but um, like those people who have read my other fics know, English isn't my first language so I might mess some things up. I do my best to correct my errors and I do proofread my chapters but some things might slip past me. And fourth: this will be a longer story. Something I don't feel comfortable doing while writing fanfiction. I think I enjoy torturing myself just a little.

So if there's something happening that you think doesn't make any sense considering the film!Avengers -universe or RotG -universe and you lose your sleep over it, then tell me! I might try to make sense out of it all. And if a character is being OOC, tell me that too and please tell me how he/she/it is being OOC. However, I will be taking some liberties but hopefully not too much. All other feedback/critique/commenting is of course very much loved too!

Also, don't worry. I am well aware of how badly I fail at romance, so that will be kept to a minimum.