Natasha Romanoff and Clint Barton seek to destroy killer-robot Ultron following a cataclysmic event.

The Watcher breaks his oath and recruits heroes from across the multiverse to battle against Ultron.

Captain America/Sam Wilson must suit up in a colossal mech suit to battle Bruce Banner after an attempt to cure himself of the Hulk goes horribly wrong. Bucky Barnes, Monica Rambeau, Moon Knight, and others must join Sam as his new team of Mech Avengers.