Loki broke into and meets with Franklin Hall,a S.H.I.E.L.D. Scientist,who tried to replicate the Super Soldier Serum before one of his experiments went wrong.
Tony Stark,Steve Rogers,and Thor were brought in by Nick Fury to show them the Cube. Then,The Frost Giants infiltrated the base,killing 3 S.H.I.E.L.D. Agents and steals the Cube. The Three Suit up and pursues the Giants until they are confronted by Piledriver and Thunderball,who are freed by Loki. Then,The Black Panther appears,killing Thunderball,But Piledriver escapes. They manage to capture Loki.
Later,They meet with Bruce Banner,along with Hank Pym,Natasha Romanoff,and Clint Barton. The Frost Giants attacks the Hellicarriers and frees Loki,who fatally stabs Veron Van Dyne.
Tony realized that Loki is having Hall making a machine. He and Steve recruited Romanoff,Barton,Banner,T'Challa,Pym, and Veron's daughter,Janet. Romanoff became Black Widow,Barton became Hawkeye,Pym became Ant-Man,and Janet became Wasp.
In New York,Loki and Hall activates the Gravitonium machine. The Heroes fought off against the Frost Giants. Ironman,Captain America,and Thor confronts Loki. While Hulk,Black Panther,Ant-Man,and Wasp fought off the Frost Giants,Black Widow holds Hall gunpoint and Hawkeye puts an arrow in the machine,causing the machine to go out of control,sucking Hall in the process before the machine is destroyed.
Hulk knocks out Loki. Thor takes Loki back to Asgard so that the Asgardians can have their memories restore. Nick Fury named the Heroes,The Avengers.
Mid-Credits:
Nick Fury was in the meeting with Charles Xavier,who also has a team.
Post-Credits:
Maria Hill tells Stark that a bunch of muggers are being webbed to the walls.