To the delight of fanboys everywhere, the official synopsis was made available Tuesday.
"When Tony Stark tries to jumpstart a dormant peacekeeping program, things go awry and Earth's Mightiest Heroes, including Iron Man, Captain America, Thor, The Incredible Hulk, Black Widow and Hawkeye, are put to the ultimate test as the fate of the planet hangs in the balance," the studios said. "As the villainous Ultron emerges, it is up to The Avengers to stop him from enacting his terrible plans, and soon uneasy alliances and unexpected action pave the way for an epic and unique global adventure."
James Spader plays Ultron, "a terrifying technological villain hell-bent on human extinction." Along the way, the unlikely supergroup will also come face-to-face with "mysterious and powerful" twins, Wanda Maximoff and Pietro Maximoff. Elizabeth Olsen and Aaron Taylor-Johnson join the cast as the siblings.
The Avengers also meet an old friend in a new form when Jarvis (Paul Bettany) becomes Vision.
The movie was written and directed by Joss Whedon and produced by Kevin Feige.
Avengers: Age of Ultron hits theaters on May 1, 2015.