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. 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 a global adventure.

For Steve Rogers, awakening after decades of suspended animation involves more than catching up on pop culture; it also means that this old school idealist must face a world of subtler threats and difficult moral complexities. That comes clear when Director Nick Fury is killed by the mysterious assassin, the Winter Soldier, but not before warning Rogers that SHIELD has been subverted by its enemies. When Rogers acts on Fury's warning to trust no one there, he is branded as a traitor by the organization. Now a fugitive, Captain America must get to the bottom of this deadly mystery with the help of the Black Widow and his new friend, The Falcon. However, the battle will be costly for the Sentinel of Liberty, with Rogers finding enemies where he least expects them while learning that the Winter Soldier looks disturbingly familiar.