Aunt Natasha and Percy Jackson
After the Giant War, only two of the Seven survived: Percy Jackson and Annabeth Chase. Deciding to take a little break from the mythology world, Percy goes home to discover something horrible. Now he has to go off and live with a long-lost aunt, who just so happens to live in the limelight.
Fury is, well, furious. Every time he gets close to figuring this case out, it slips through his fingers like water. When he finally does solve it, he delves further into Natasha Romanova/Romanoff's past than he thought possible. He discovers she has a nephew. And this nephew, is his target.
A PJO/Avengers crossover. Natasha has now become an aunt.
Troubles awaiting. And maybe, just maybe, Percy knows more about this than he lets on.
WARNING: fangirl Thor.