Disclaimer: I don't own Doctor Who or the Avengers. Just in case there was any confusion on the meaning of fan fiction.
"Do you… speak?"
The fairies all spoke at once. "We do."
Natasha narrowed her eyes, trying to determine the best way to address them. She expected they wouldn't fall for the weak little girl trick, so she decided to be a little more direct. "Why are you attacking?"
"You killed our child."
"I did not."
A couple fairies hissed. "Our child died in your battle."
"The Chitauri attack? That wasn't our fault."
"The others in the fight have already paid the price. The foreigners."
Natasha nodded, getting a feel for the way the fairies talked. "The Chitauri instigated, we were defending. You should be going after their leader."
"We saw no leader."
"His name is Loki of Asgard. But he's not on this planet right now. You'll have to go find him."
There was some indistinct whispering amongst the fairies, then they began to fly away. "When we're done with him, you shall see us again."
The TARDIS appeared and the Doctor stepped out. "I'll… handle this. Where'd they go?"
Natasha rolled her eyes. "I took care of it."
Tony smirked at the Doctor. "See? We didn't need you after all."
"Actually, his police box saved your life," Steve said.
"Boys." Natasha pointed at the cell's control panel.
"What if we just left her in there?" Tony suggested.
"What if I pulled out your reactor?"
The Doctor waved the sonic screwdriver at the door and it popped open with a hiss.
"Well, I'd say it's about time I went." The Doctor waved half-heartedly at Natasha. "Before SHIELD gets any ideas. Steve, Pepper, always a pleasure. Stark, out of my TARDIS and don't make a laser screwdriver. They're nothing but trouble." Having shooed the humans out of his ship, the Doctor closed the doors and the TARDIS disappeared.
And that's the end.