One of Walter's subjects is young Olivia Dunham, aka "Subject 13". Walter suspects Olivia's stepfather is abusing her based on scars she carries and frightening drawings in her sketchbook, but Olivia refuses to talk about it. One night, as Olivia is about to be struck by her stepfather, she temporarily finds herself in a different place; the next day, she draws what she saw in her book, a zeppelin. Walter realizes that Olivia crossed over to the parallel universe, and can be the means for returning Peter. Walter puts Olivia under several tests to try to coax her ability to cross over, eventually eliminating all but fear as catalysts. He arranges a traumatic test for Olivia, but instead of crossing over, she exhibits pyrokinesis and sets the room afire. In the confusion in putting it out, she disappears.
Peter, discovering a picture of white tulips in Olivia's book, is able to find her nearby. After they introduce themselves, Olivia admits to being scared of going home to her stepfather. Peter tells her to trust Walter and face her fear, and then returns her to the child care center to everyone's relief. As Olivia waits for her stepfather, she draws her and Peter into her book. As he is about to arrive, Olivia decides she must tell Walter about him, and rushes to his office. Olivia, in tears, hands Walter the sketchbook, explaining about her stepfather's abuse and that she knew she had crossed over to the parallel universe. She is interrupted by a sound from behind her: it is Walter. Olivia had temporarily entered the parallel universe and spoken to Walternate. Walter takes Olivia to her stepfather, but warns the man that he will be reported to social services if Olivia is harmed again.
Elizabeth and Peter return to Reiden Lake, and Peter eventually comes to call Elizabeth his mom, but Elizabeth becomes forlorn after she realizes the lie she has been maintaining for the last few months. The episode ends in the parallel universe, where Walternate has reviewed Olivia's sketchbook, including her latest picture of her and Peter; now aware of the parallel universe, Walternate gains new resolve to get his Peter back.