Fringe/Recap/S02 E15

Season 2, Episode 15:

Jacksonville
In Manhattan, a building from the alternate universe is transported into the prime universe, merging with its counterpart with catastrophic consequences for everyone inside: one man finds himself fused together with his counterpart and somehow still alive despite suddenly having too many limbs and organs. As Olivia investigates and learns that Newton is responsible, Walter theorises that due to the method used to cross one building over to the other side -- based on the original methods used in Walter and William Bell's earliest experiments in which objects of equal mass in both universes swap places -- a building from the prime universe Manhattan will disappear into the alternate universe with the space of a day or so.

To identify the building that will disappear and save the people inside, Walter suggests that he and Olivia revisit the cortexiphan experiments from over twenty years ago, which had allowed her to identify objects from the other side (by their "glimmer") and even travel between the two universes. Since the ability was dormant, Walter tries to reawaken it with a fresh dose of cortexiphan. The ability is subsequently triggered by Olivia's emotions, specifically fear, but the result of a lifetime's worth of physical, mental and emotional abuse has caused her psyche to harden to the point of being fearless. Considering the experiment a failure, the Fringe team return to New York and work with Massive Dynamic to try and identify the building using other means, such as identifying a building with the exact same mass as the one that appeared from the other universe.

As the expected time of the building's disappearance draws closer, Olivia becomes increasingly guilty over the failure of the cortexiphan experiment and afraid for the people she's unable to save -- which triggers the ability and allows her see the "glimmer" of the other side and identify the building. The FBI evacuates just in time, so that there are no casualties when the building disappears. Later, Olivia goes to the Bishops' house, planning on going out for celebratory drinks with Peter. When she sees the glimmer around Peter, she realises that he's from the alternate universe. Walter begs her not to tell Peter.