This is my first time writing for Avengers and this specific pairing, and I've only seen The Avengers and Iron Man so my apologies in advance if the characters are slightly out. I do not own any characters mentioned in this fanfiction.

The almost simple looking, unused invention sat on Tony's clustered desk, waiting to be tested. Unlike the old model, Stark focused intently and worked longer on making the improved paralysis device less hostile. It may have been several years since the incident with Stane, but the sonic weapon sitting idle in front of him brought back vivid memories of that near-fatal day. But that was the old model. Since before sunrise the previous day, he had shut himself away in the harsh white artificial lights of the laboratory, bringing up the almost ancient plans and recreating the somewhat banned device.

Less than eight hours of solid work time and Tony held the black, taser-like object in his tired hands, turning it over and imagining the use of it in combat. Of course, he'd need to test the effectiveness before launching himself into a fast paced mission with it in hand, or passing it over to Natasha or someone else to use. The device may not even work properly. It may be too powerful and completely disable someone's involuntary bodily functions. That wouldn't turn out so good. If the new invention was anything else, Tony would have been confident of success after running the prototype by a few lab tests; but this was different. The last time that a paralysis was used around him, he was crawling through his lab on the brink of death, not sure if he would live to see another sunrise.

Stark wandered briskly out of his lab and down the twisting corridors and staircases to the entrance of HQ. Instead of testing on any person, the engineer decided on acquiring mice. Being one of his least favorite methods of experimentation, he didn't have a fresh supply of cheese-eaters living under his workbench. Besides, he'd kept a couple of the furry critters during an exceptionally lonely period in his early adulthood, and he'd feel bad if he was physically hurting some distant cousin of Cheesecake. But what could go wrong with this? It was one of the few devices Tony had made for self defense and for public distribution. No, it wasn't intended to be a weapon. It was virtually harmless; if it worked.

Steve Rogers walked slowly and awkwardly, still in his 'work' outfit, through the ground level of headquarters. He'd sustained a concentrated beating to one of his shins while out on a city-based mission. It wasn't too bad, but there was an exceptional amount of blood. It would bruise and hurt like hell in a few short hours. The Captain kept walking, glad to soon be slipping out of his suit and into a needed shower. He was even gladder to see Tony walking towards him; a friendly face after a solo mission was always a relief.

"Mr Stark," Steve greeted Tony as he approached, pulling the cowl from his head. "Heading off without the suit?"

"Just need to pick up some friends, then throw them in a cage and poke them with toothpicks for awhile," Tony replied bluntly. A mix of confusion and horror appeared on the Captain's face.

"Mice, Steve. I'm getting mice."

"Oh, yeah, I knew that."

"Don't worry, I sure wouldn't mind throwing you in a cage and poking you with something," the engineer winked back with a grin. Steve huffed impatiently, but then stopped walking and faced Tony directly.

"This is for testing your new invention, isn't it?" Rogers asked, sounding interested but suspicious.

"I wouldn't call it completely new, but yeah. How did you know about that? Been spying on me this morning, have you? Been watching me shower, too?"

"Pepper told me well, everyone about how you're finally making something for a more widespread use. And about your previous backfire with the para- the paraly- paraliz- para-"

"Paralysis."

"That. Why'd you bring it back? I thought it was banned. Illegal, even. Wouldn't want Fury-"

"Don't worry, tiger, I got this. It's not as..." Stark winced at the memory, "...painful as the old one."

Steve lowered his eyes, a little drop of a guilt running down his spine. It was no doubt a sensitive topic. But before Rogers could duck away and get back to his room, Tony grabbed his shoulder, a puppy-dog look appearing on his face. The Captain wasn't ready for what the engineer suggested. He was slightly taken back when he said yes.

"Are you sure this is safe?"

"For the tenth time, yes. And in case something goes wrong, the safety word is 'sex god'. Now you just lie there and look sexy. Simple enough?"

Tony taped the second node to the Captain's chest as he nodded and rolled his eyes. The monitor quickly responded, numbers appearing above the heartbeat sensor, counting Steve's breathing rate. In the lab he felt safe, confident even, that the shirtless soldier lying on the flat metal desk would come out of this with all his limbs intact and functional.

However, when Stark clipped open the sonic device's case and realized exactly what he was doing, his confidence haltered. He tried hard to wipe away the fear. It was safe, it definitely was. It had to be. He'd figured it all out, calibrating it perfectly. But still his mind wandered and he saw the soldier lying rigid and in pain, his eyes red and his skin gray and feeling as close to death as Tony had under the assault of Stane. Rogers probably felt safer than the experiment conductor did; after all, ignorance is bliss. If something terrible were to happen to the Captain, Tony wouldn't move on. He stayed clear of that thought, focusing instead on the test.

The billionaire looked down at Steve lying in wait.

"I really wonder how the monitors pick up your heartbeat under so much muscle," Tony teased, shamelessly flirting as always. Steve was far more than use to it by now, but the remark didn't hide the obvious nervousness in the other man's voice.

The Captain caught the eye contact of Tony and held it. "Listen, I'm more than happy to help you, even if it is the stupidest thing I've ever done. I know this is risky. If you want to do this some other time, I can-"

"Nervous? You think I'm nervous with testing my own equipment? I add all sorts of things to the Iron Man suit, no idea if they'll work or not." He rechecked the medical and scientific equipment connections and turned on the ominous device. "Besides, this is in a lab. My lab, in fact. With me. Safest place on Earth."