There's a virus spreading around the Avengers tower and it seems to make people no longer themselves, seeing as they all have contracted some kind of illness. You are the only one not effected and are now in charge of figuring out what has happened and to stop the virus.
(Effects Of virus play against a characters strengths. For example for Tony Stark he'd never be able to think straight and can't be the genius he is or Captain America wouldn't be able to tell right from wrong even though he tries extremely hard to be right)