Fringe Season 3 Episode 15 (02/25/11)
Flashback to 1985. Young Peter is trying to return to his own world via Rieden Lake by dropping a cinder block into the ice, tied around his waist. Elizabeth dives in after him and saves him.
Walter is working with a group of children, including Olivia, when he gets a call that his wife is in town. Peter is adamant that they are not his parents and the Bishops do everything to try to soothe him and prove otherwise.
Olivia is running from her stepfather as he chases her in anger and she flashes to another place for a brief second. Walter's experiments on the children are working. He may find a way to transport Peter home.
Olivia shows up at school the next day with a black eye, and she tells Walter she fell running in her house. She is drawing a Zeppelin; she has flashed to the other world. Walter tries a myriad of experiments to test which emotional state will put Olivia into the place she needs to be to transfer. It's not exhilaration, anger or loneliness. Walter sets up an elaborate test to scare Olive half to death. It works. When Olivia goes missing, Peter flips through her things. From a drawing, Peter knows where to find her and goes to her.
Flash to Walternate and Elizabeth dealing with the aftermath of Peter's kidnapping. Walter is drinking heavily.i Elizabeth saw Walter take Peter away, and Walternate is trying to determine why she didn't recognize it was something he would wear. They consider that the kidnapper had plastic surgery. Their marriage is in turmoil and Elizabeth won't let it fall apart as they await the miracle of his return.
Peter finds Olivia and brings her back. He talks her into trusting Walter to help her with her stepfather. In a frightened rush, she runs into his office and asks him to help her stepfather stop hitting her. Except she has flashed and is talking to Walternate. When Walter appears in the room, he is unaware she had flashed. Walter confronts her stepfather to leave her alone or else.
Peter questions Elizabeth about her being his real mother, and she lies. The pain this causes her is visible.
Flash to the other universe, and holding the picture book Olivia thought she gave to Walter is in Walternate's hands. He now understands the two universes.