1945 and during a raid on the last stronghold of Nazis who are being aided by an extraterrestrial race, Captain America clambers onto and destroys their secret weapon, a nuclear missile headed for Washington D.C., sacrificing himself in the process.

Present day: Captain America is found by S.H.I.E.L.D., cryogenically preserved in an artic glacier. He is brought back to America, thawed and revived in the hope that the “Super Solider” serum that gave him his abilities can be recreated. While Bruce Banner tries to unlock the formula, hindered by his anti-Hulk medication, the alien attacks a space satellite and shuttle, resulting in General Nick Fury being ordered to put backup plan Operation Avenger into effect. Fury heads to recruit Giant-Man, Wasp, Iron Man and Thor to form a group that can face the alien threat under the leadership of Captain America; but can this group of fiercely independent superheroes act as a team?