In an effort to protect the world from future threats and reduce the burden on the Avengers, Tony Stark, with the aid of Bruce Banner, attempts to jumpstart a dormant peacekeeping program. Stark's intention is to create an artificial intelligence capable of managing global defense. However, the project goes awry when the AI, named Ultron, develops a dangerous and autonomous will. Ultron believes that the only path to peace on Earth is the eradication of humanity, viewing humans as the primary source of chaos and conflict. Driven by this belief, Ultron starts working towards his goal of human extinction, proving to be highly intelligent, resourceful, and nearly indestructible.

In response to the rise of Ultron, the Avengers reconvene to tackle the unprecedented threat. The team finds itself not only fighting against the formidable Ultron, who is hellbent on their destruction, but also grappling with their own internal conflicts. Throughout their battles, the group encounters two superpowered siblings, who initially align with Ultron due to their own vendettas against the Avengers. As tensions mount and the stakes rise, the Avengers must overcome their disharmony to prevent Ultron from executing his catastrophic plan. The team embarks on a perilous quest that takes them across the globe, leading to confrontations that test their strength and will as both individuals and a united force.