Release date: 4 May 2013, United States
As with all overviews, ALL THE SPOILERS ahead.
A mysterious alien artifact called the Tesseract summons the Asgardian god Loki to the Earth, where he uses a powerful staff to either kill or enthrall several S.H.I.E.L.D. operatives before stealing the Tesseract and making his escape with them. The head of S.H.I.E.L.D., Nick Fury, gains permission from a shadowy council to assemble a team of superheroes (Iron Man, Bruce Banner, Black Widow, and Captain America) code named The Avengers Initiative to help capture Loki and recover the Tesseract. They find and capture him in Berlin but his operatives get away with a cache of rare metals. Loki’s brother Thor shows up to claim him but after fighting Iron Man and Captain America, Thor agrees to let Loki remain captured in S.H.I.E.L.D.’s helicarrier.
Loki’s operatives trace him and sabotage the helicarrier to free him as Banner becomes the Hulk and goes on a rampage through the vessel. Through fierce combat and resourcefulness, the helicarrier is saved from crashing, but Loki escapes with his staff.
In New York City Loki’s operatives use the metals they stole and the Tesseract to create an interdimensional gate through which he summons an alien army. Though the Avengers mount a strong defense of the city, the shadowy council orders a nuclear strike on the city to destroy the alien army. Iron Man intercepts the missile, flies it through the portal into the alien mothership, disabling the invaders em masse before falling back through the portal to Earth.
At the resolution of the film, Thor returns to Asgard with Loki and the Tesseract and the staff remains on Earth. Also the team enjoys some shawarma.