realizes they are going to New York City to fulfill Booker's debts, Elizabeth knocks him out and flees. Booker awakens to find the airship under the control of Daisy Fitzroy, who offers to return the ship if Booker helps her arm the Vox Populi. Booker and Elizabeth join forces to secure weapons from a local gunsmith. Traveling through Tears, they arrive in a world where Booker is a Vox Populi martyr and open warfare has erupted in Columbia. Elizabeth kills Fitzroy to prevent her from executing a Founder boy. Songbird attacks the duo as they try to flee Columbia, and their airship crashes back to the city. Elizabeth and Booker discover a conspiracy behind the city's founding: Elizabeth is Comstock's adopted daughter, whom he plans to groom into Columbia's leader after his death. Comstock killed his wife and the Luteces to hide the truth, and installed a siphon in Elizabeth's tower to limit her power. Elizabeth is recaptured by Songbird. Pursuing her, Booker is brought forward in time to New Year's Eve of 1983 by an elderly Elizabeth as Columbia attacks New York City. This Elizabeth returns Booker to 1912 with information on controlling Songbird, in hopes he can save her younger self and erase the torture and brainwashing she suffered. Booker rescues Elizabeth, and the pair pursue Comstock to his airship. Comstock demands that Booker explain Elizabeth's past to her, and the two begin to argue; an enraged Booker drowns Comstock in a baptismal font. Booker denies knowledge of Elizabeth's past, but she asserts that he has simply forgotten. Booker and Elizabeth direct Songbird to destroy the Siphon, unlocking Elizabeth's full powers. Elizabeth opens a Tear and transports them to the underwater city of Rapture. The newly aware Elizabeth explains there are countless alternate lighthouses and versions of Booker and Elizabeth; their reality is one of an infinite number depending on their choices. She shows that Robert Lutece approached Booker on behalf of Comstock to acquire Booker's infant daughter, Anna DeWitt, in exchange for erasing his debts, as Comstock was rendered aged and sterile as a result of exposure to Tears. Booker attempted to take Anna back from Comstock, but the closing Tear severed Anna's finger. Comstock raised Anna as his own daughter, Elizabeth; her severed finger, which caused her to exist in two realities simultaneously, is the source of her ability to create Tears. Robert Lutece, angry at