Avengers: Age of Ultron begins in the Eastern European country of Sokovia. The Avenger team of Tony Stark, Steve Rogers, Thor, Bruce Banner, Natasha Romanoff, and Clint Barton raid Baron Wolfgang von Strucker’s Hydra outpost. He’s been busy experimenting with Loki’s captured scepter on humans.
The Avengers come across two of those experiments in the Maximoff twins. Pietro has superhuman speed, and Wanda has telekinetic abilities she uses to manipulate minds. Rogers nabs Strucker in the raid, as Stark goes after the scepter. However, Wanda is able to implant a vision of a terrible future in his mind.
Back at Avengers Tower, Stark and Banner discover an artificial intelligence housed in the scepter’s gem. They secretly decide to use it for Stark’s “Ultron” global defense program. However, once they leave for a party, the program comes to life.
When Ultron wakes, he believes that he must destroy humanity to save the Earth. Ultron takes out Stark’s AI, JARVIS, and uploads himself into one of Stark’s Iron Legion robot drones to attack the Avengers after the party. He then leaves with the scepter in hand, and goes to Strucker’s Sokovia base to upgrade his own body, and also build an army of robot drones.
Once there, he first kills Strucker, and then recruits the Maximoff twins to help him with his plan. It’s easy to convince them to help as the twins believe Stark is responsible for their parents’ deaths after the weapons his company made were used to kill them.
The three then find arms dealer Ulysses Klaue at an African shipyard to pick up some Wakandan vibranium. The Avengers tail them there, but Wanda is able to implant her own haunting visions into everyone’s minds except for Stark and Barton. Banner’s vision causes him to turn into the Hulk, and he begins rampaging through a nearby city until Stark can stop him in some Hulk-busting armor.
This results in a worldwide backlash over against the team, and they go into hiding at Barton’s safe house. There, they meet his wife and children for the first time. His family was previously unknown to them all except for Romanoff.
Thor soon leaves the team to meet with Dr Erik Selvig on the meaning of the apocalyptic future his vision showed him. Romanoff and Banner, who are mutually attracted to one another, discuss the feasibility of leaving the team to be together. Soon, Nick Fury shows up, and convinces them to all stop being pussies, and fight back to stop Ultron.
Ultron heads to Seoul to force Dr. Helen Cho to use her synthetic-tissue technology in combination with the vibranium and the scepter’s gem to create a new body for him. While Ultron is distracted uploading himself into his new synthetic body, Wanda takes the time to read his mind. When she discovers his plan to destroy all humanity, the Maximoffs decide to turn on Ultron.
They join forces with Rogers to form a distraction while Romanoff and Barton steal his synthetic body. Unfortunately for the Avengers, Ultron captures Romanoff. Barton reluctantly abandons her to get Ultron’s body back to the Avengers Tower. Rogers and the twins soon show up without Romanoff too.
As the Avengers take the time to argue amongst themselves, Stark finds JARVIS hiding in the internet, and uploads him into Ultron’s synthetic body; becoming the Vision. Thor returns in the nick of time to help activate the body. He reveals that the gem on the Vision’s forehead is one of the six Infinity Stones; the most powerful objects in the universe.
The Vision proves his worthiness to the team when he lifts Thor’s hammer. He and the Maximoff twins head back to Sokovia with the Avengers. Ultron is there to use the remaining vibranium to build a machine that is able to lift a large part of the capital city into the sky. He intends to crash it into the ground, and cause a global extinction. Banner is able to rescue Romanoff, and she then pushes him into a pit to get him to turn into the Hulk for the upcoming battle.
The Avengers take on Ultron’s army, as Fury shows up in a Helicarrier with Maria Hill, War Machine, and several other SHIELD agents to help evacuate the civilians. Meanwhile, they task Wanda to keep Ultron’s drones from activating the machine. When Ultron manages to steal the Avengers’ Quinjet, he uses it to stop the evacuation.
Pietro dies from shielding Barton from Ultron’s gunfire. Then, the Hulk leaps into the Quinjet, and forcibly removes Ultron from it. Seeking vengeance for her brother’s death, Wanda abandons her post to destroy Ultron’s body. Unfortunately, one of his drones manages to activate the machine.
The city plummets to the earth, but Stark and Thor are first able to overload the machine, and then destroy the massive piece of land. The Vision swoops in to rescue Wanda before she’s killed. The Hulk sets out in the Quinjet to go into hiding; abandoning Banner’s dream to live happily ever after with Romanoff. The Vision then cleans up by destroying Ultron’s last remaining body.
The Avengers soon set up a new base which Fury, Hill, Cho, and Selvig will run. Barton returns home to his family. Thor returns to Asgard to learn more about the shadowy figures manipulating recent events behind the scenes, and Stark leaves the team maybe forever. Rogers and Romanoff begin training a new team of Avengers comprised of James Rhodes, the Vision, Falcon, and Wanda.
In a mid-credits scene, Thanos has tired with the lack of progress in obtaining the Infinity Stones. He slides into the Infinity Gauntlet, and vows take the Stones himself.