Eighteen months after the destructive battle with General Zod in Metropolis in Man of Steel, Superman has become a controversial figure. Billionaire Bruce Wayne, who has operated in Gotham City as the vigilante Batman for nearly two decades, sees Superman as a potential threat to humanity. After learning of Batman’s form of justice, Clark Kent, Superman’s alter-ego, seeks to expose Batman via Daily Planet articles. Wayne learns that Russian weapon trafficker Anatoli Knyazev has been contacting LexCorp mogul Lex Luthor. Meanwhile, Luthor unsuccessfully tries to persuade Senator June Finch to allow him to import kryptonite retrieved from the Indian Ocean following Zod’s terraforming attempt, claiming he wants to maintain it as a “deterrent” against Kryptonians. He instead makes alternative plans with Finch’s subordinate and gains access to Zod’s body and the Kryptonian scout ship.
Wayne attends a party at LexCorp, where he meets an antiquities dealer named Diana Prince, and retrieves encrypted data from the company’s mainframe. While decrypting the drive at the Batcave, Wayne dreams of a post-apocalyptic world, where he leads a group of rebels against a fascist Superman. He is snapped out of the vision by an unidentified being who warns him of Lois Lane’s crucial role in the future, and urges him to find “the others” before vanishing. Wayne later discovers that Luthor is not only experimenting with kryptonite, but also investigating metahumans. One of them is Prince herself, who is an immortal warrior. Wayne admits to Alfred Pennyworth that he plans to steal the kryptonite to weaponize it, should it become necessary to fight Superman.
At a congressional hearing, as Finch questions Superman on the validity of his actions, a bomb goes off and kills everyone present but Superman. Believing he should have detected the bomb, and frustrated by his failure to save the people, Superman goes into self-imposed exile. Batman breaks into LexCorp and steals the kryptonite, planning to use it to battle Superman by building a powered exoskeleton, and creating a kryptonite grenade launcher and a kryptonite-tipped spear. Meanwhile, Luthor enters the Kryptonian ship and accesses details of a vast technology database accumulated from over 100,000 worlds.