Sabotage(Black Widow)

When Black Widow stumbles across a old S.H.I.E.L.D headquarters on her mission to find Hulk, she finds old files of a completed sabotage mission.

Tony Stark is trying to run his company but his separation from Pepper is hard on him. So when a evil comes and takes over he is powerless to stop it.

Captain America is called back to help along with Falcon but he doesn't want to leave Bucky without a cure.

With so many problems to fix the superheroes won't be able save the day without some help. Unfortunately the only help available are superheroes that disappeared long ago.

I don't own any of Marvel's characters or superheroes except the ones I made up.