In the Eastern European country of Sokovia, the Avengers – Tony Stark, Steve Rogers, Thor, Bruce Banner, Natasha Romanoff, and Clint Barton – raid a Hydra facility commanded by Baron Wolfgang von Strucker, who has been experimenting on humans using the scepter previously wielded by Loki. They encounter two of Strucker’s test subjects – twins Pietro Maximoff, who has superhuman speed, and Wanda Maximoff, who can manipulate minds and project energy – and apprehend Strucker, while Stark retrieves Loki’s scepter.
Stark and Banner discover an artificial intelligence within the scepter’s gem, and secretly use it to complete Stark’s “Ultron” global defense program. The unexpectedly sentient Ultron, believing he must eradicate humanity to save Earth, eliminates Stark’s A.I. J.A.R.V.I.S. and attacks the Avengers at their headquarters. Escaping with the scepter, Ultron uses the resources in Strucker’s Sokovia base to upgrade his rudimentary body and build an army of robot drones. Having killed Strucker, he recruits the Maximoffs, who hold Stark responsible for their parents’ deaths by his weapons, and go to the base of arms dealer Ulysses Klaue to obtain Wakandan vibranium. The Avengers attack Ultron and the Maximoffs, but Wanda subdues them with haunting visions, causing the Hulk (Banner) to rampage until Stark stops him with his anti-Hulk armor.1
A worldwide backlash over the resulting destruction, and the fears Wanda’s hallucinations incited, send the team into hiding at a safehouse. Thor departs to consult with Dr. Erik Selvig on the meaning of the apocalyptic future he saw in his hallucination, while Romanoff and Banner plan to flee together after realizing a mutual attraction. However, Nick Fury arrives and encourages the team to form a plan to stop Ultron. In Seoul, Ultron forces the team’s friend Dr. Helen Cho to use her synthetic-tissue technology, together with vibranium and the scepter’s gem, to perfect a new body for him. As Ultron uploads himself into the body, Wanda is able to read his mind; discovering his plan for human extinction, the Maximoffs turn against Ultron. Rogers, Romanoff, and Barton find Ultron and retrieve the synthetic body, but Ultron captures Romanoff.