With S.H.I.E.L.D. destroyed and the Avengers needing a hiatus from stopping threats, Tony Stark attempts to jumpstart a dormant peacekeeping program with Ultron, a self-aware, self-teaching, artificial intelligence. However, his plan backfires when Ultron decides that humans are the main enemy and sets out to eradicate them from Earth, and it is up to Iron Man, Captain America, Thor, the Hulk, Black Widow and Hawkeye, along with support from Nick Fury and Maria Hill, to stop him from enacting his plans. Along the way, the Avengers encounter the powerful twins, Pietro and Wanda Maximoff, as well as the familiar Vision.