No one else knew what Tony and Bruce's latest mad science project was supposed to do, but the actual result of the first test run was a shockwave of energy that rippled through the entire tower, knocking everyone inside to the ground but somehow avoiding any structural damage to the building itself. There were a dozen or so jammed wrists and a few scattered reports of synesthesia, but all in all they seemed to have gotten off remarkably lightly.
Naturally, it was just as everyone was dusting themselves off and meeting up to share that conclusion that JARVIS spoke up.
"Excuse me, sir, but I have been scanning all occupants of the building for injury and Ms. Lewis no longer matches the baseline record I have stored for her. While previous scans and records indicate her to be a biologically normal human, the current scan is detecting a significantly depressed core temperature and two separate heartbeats, both of which are registering at a resting rate that is well above what should be the maximum for a woman of her age."
"Hey," Darcy snapped automatically as the others turned to stare at her, "lay off the age! When 500 years old you reach, look this good you will not!" Then she froze, and very slowly looked back over her shoulder at the assembled Avengers who happened to be in the room. Thor didn't look like 500 years was anything to get upset about, Tony wasn't wearing the armor, and Bruce had gone to the kitchen to find something to get the taste of mauve out of his mouth, but Natasha and Clint already had weapons drawn and Steve was flexing his hand on the grip of his shield.
Fortunately, she'd already been holding her sonic iPod, and a quick swipe of the clickwheel was enough to activate the emergency transmat. This was going to take so much explaining.
Chapter 2: Totally Stark's Fault
Original prompt: Sometime between graduating high school and becoming Jane's intern, Darcy traveled with the Doctor.
(I completely failed to include the OP's request for SHIELD vs. UNIT because I got distracted by the Darcy+Taser OTP. No shame!)
Really, it's all Stark's fault.
Because honestly, how the hell does the man sneak up on a girl when he's wearing a giant robot suit?? It's not fair, you either get ninja skillz or ridiculous combat abilities, but never both- Natasha is an exception, because Natasha is an exception to everything (seriously, sometimes Darcy thinks that if she'd stuck with the Doctor just a little bit longer they would have ended up on the planet where there were factories producing the ultimate fighter, a mix of 50% superspy and 50% special forces, with an extra 100% badass thrown in on top, and they would have been called the Widowbot 9000 or something, and then the Doctor would have blown up the factory and there would have been lots of shouting and running and revolution), but regular humans have to choose one or the other. Adding a stealth mode to your crazy flying man-tank is obviously cheating.
So it's definitely Stark's fault. Because if he hadn't snuck up on her (snuck, walked, po-tay-to, po-tah-to; she was clearly wearing headphones and not expecting an armored billionaire to come up behind her, it doesn't matter if she was sitting in the common lounge in his
giant phallic symbol tower or not) then she would not have been forced to react on instinct and shock his ass into a drooling pile of red and gold.
Look, a girl has reflexes, all right? A metal hand comes out of nowhere and lands on your shoulder, you do not wait for it to start talking about deleting people before you set your (slightly sonic-souped-up) Taser to 'cyber' and let loose. Totally Stark's fault.
Coulson actually smiled when he heard, honest to Thor or your deity of choice. (Which probably rules out another space factory producing the Suitbot 9000, but she's not eliminating the possibility completely.) She's definitely getting that postgrad position she applied for last week. Win!