As the Songbird turns on Booker again, Elizabeth's powers fully awaken, allowing her to open a Tear and transport them to the underwater city of Rapture. [b] Booker and Elizabeth materialize inside the city, from where they see the Songbird crushed outside by the water pressure. Elizabeth takes Booker to the surface lighthouse, explaining there are countless alternate lighthouses and versions of Booker and Elizabeth; they are within one of infinite possible realities dependent on their choices. She shows that on October 8, 1893, Robert Lutece approached Booker on behalf of Comstock, requesting that he "bring us the girl and wipe away the debt," referring to Booker's infant daughter, Anna DeWitt – Booker's "AD" branding. Booker reluctantly agreed, but, having changed his mind, soon gives chase; Comstock barely escaped through a Tear, and its closing severed Anna's finger. Comstock then 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 Comstock's actions, convinced Rosalind to help him bring Booker to the reality where Columbia exists to rescue Elizabeth. It is also revealed that Booker in fact willingly agreed to come to Columbia to save his daughter, but the mental strain of crossing dimensions caused him to rewrite his own memories such that he combined giving Anna away with his attempt to secure Elizabeth.