After the Avengers take out a Hydra base that was coveting Loki's staff, Tony Stark takes it upon himself to use the infinity stone that they uncover to active a dormant program to help protect the earth known only as Ultron. But like most science fiction films dealing with creating intelligent life with machinery, something goes horribly wrong to where the Avengers have to stop it. Oh and there's these three new members that are introduced along the way, and Hulk apparently has a thing with Black Widow. Who knew?