Master assassins (though Hawkeye is initially brainwashed by Loki). Thor: The God of Thunder who arrives to stop his brother. The Conflict
The team initially struggles to work together. Their clashing egos and Loki’s manipulations lead to a massive confrontation aboard the S.H.I.E.L.D. Helicarrier. After the tragic death of Agent Phil Coulson, the heroes finally find a common cause and realize they must stand together to save the world. The Battle of New York
A scientist with a gamma-powered temper.
It sounds like you're looking for the plot of the 2012 blockbuster . Here is the story breakdown: The Threat