In the parallel universe, Olivia undergoes an experimental treatment in order to replace her memories with her alternate counterpart, and then find a way to transport between universes. She manages to escape and takes taxi driver Henry (Andre Royo) hostage. To return to her universe she goes to the same opera theatre used in "Over There", but arrives in time to see it ambered. Throughout the episode it is revealed that despite the experiment's initial failure, “Walternate” realises that it is slowly succeeding thanks to the adrenaline Olivia produced evading the alternate Fringe Division. Olivia remembers a safehouse and goes there, which turns out to be the home of her mother, Marilyn (Amy Madigan) who died in the prime universe; Marylin convinces Olivia that she suffered a mental breakdown. Now the experiment has succeeded, she returns to Fringe Division. Meanwhile in the prime universe, Walter and Peter prepare to move on with their lives, with neither seeming to suspect the Olivia with them is in fact her alternate counterpart in disguise.