When Tony Stark and Bruce Banner begin working on a worldwide peacekeeping system, things go very wrong, and Earth's Mightiest Heroes - Iron Man, Captain America, Thor, Hulk, Black Widow and Hawkeye - are put to the ultimate test. The evil Ultron threatens the fate of humankind and it is up to the Avengers to stop him. Uneasy friendships and unexpected action make for an epic adventure.