Security guards at Elias Cryonics-Research and Storage Company load cryogenically frozen heads onto a secure truck. A man, Smith, pulls up in a car and asks for directions. The guards order him to leave, but Smith just exits his car and begins to shoot. One guard turns out to be his accomplice and throws Smith a set of keys to the truck. Smith drives off as his accomplice is shot multiple times before being killed-what's this guy made of?! He bleeds silver.
At the site, Broyles debriefs the Fringe team. This is the third robbery of a cryogenic facility this week. Walter begins to examine the guard's body that was bleeding mercury. As he is taking samples of his blood, he finds a conversion device similar to the one found on the shapeshifter who tried to kill Olivia. This one, however, is fully intact.
Smith meets with Shapeshifter Charlie as he goes through all the frozen heads-looking for a certain head, but they are unsuccessful. Charlie warns Smith that the FBI understands who they are. Charlie explains that he has requested extraction but they will not extract him until he finishes his mission to get information from Olivia, but he has had no luck getting her to remember what happened in the parallel universe.
At the lab, Walter studies the body of the guard that was bleeding mercury. He finds that the shapeshifter has mercury in his blood. The blood sample from the shapeshifter who attacked Olivia weeks ago was normal. This means that the shapeshifter has taken on another body and is still after her.
Olivia takes the shapeshifter conversion device to Nina. Peter works with a scientists at Massive Dynamic and they have determined that it streams data and that the device stores a pattern off their last victim. Nina informs Olivia that each shapeshifter is assigned a specific device, and if they use the new conversion device to fix the one found on the shapeshifter who attempted to kill Olivia, they will be able to find out who he or she is.
Walter and Peter visit Rebecca-a women that was able to identify shapeshifters years ago in Walter's lab-in hopes that she still has the ability to detect shapeshifters. She tells them that she used to be able to detect shapeshifters by their glow, but her ability has faded. Walter's experiments triggered her ability to see beyond the limits of vision. Rebecca agrees to be experimented on again to see if her ability to detect shapeshifters can be restored.
Walter takes Rebecca back to the lab to experiment on Rebecca. Peter rings a bell to as part of the experiment but this bell causes Olivia to collapse and seize. During this time, she begins to be flooded with memories from the parallel universe.
In her memories, William Bell warmly greets Olivia at the World Trade Center happy to see her after all these years. He warns her that a war is coming. He informs her that the "first wave" is already in our universe. Although only a handful of people from our universe have crossed over to the parallel universe, they have created hybrids that are part machine and part organic tissue that have the ability to cross over easily and to change shapes taking the forms of human beings. He also informs Olivia that the leader of the shapeshifters has an omega symbol hidden on him. She must find him before the shapeshifters do because he holds the power to open the door between the universes!! He and Walter experimented on Olivia years ago in order to prepare a guardian to watch the gate between the two worlds. If she does not find him before the shapeshifters, the end will come. William Bell hits a bell before sending Olivia back to her universe. She crashes through the office window and back to present time.
Olivia visits Nina Sharp to inform her of her recent memories. Meanwhile back at the lab, Charlie discovers the computer on the Massive Dynamic website as Nina explains a theory William Bell had about the last great storm. If the door was open between the two universes, only one world would survive. Olivia suddenly has a flash memory of William Bell holding a piece of paper reading Laston Hennings Cryonics. Olivia is about to tell Nina about her vision when she receives a text message from Charlie saying "It's Nina. Don't Trust Her. Get out now." Olivia quickly gets up and exits.
Outside Massive Dynamic, Charlie ushers Olivia to come with him. Olivia tells Charlie that she remembered where the head of the leader is located and tells him the location. She opens her phone to call when the image from Massive Dynamic is uploaded to it. A picture of Charlie emerges-HE IS THE SHAPESHIFTER! Charlie knocks Olivia down and calls Smith to give him the location. Olivia rises up and shoots at Charlie until he is killed.
Walter takes Rebecca back to her home and apologizes to her for experimenting on her years ago. She, however, thanks him for making her special. Walter responds by telling her she was always special to him.
Meanwhile, Broyles consoles Olivia who is consumed with guilt for killing Charlie. He reminds her that it was not Charlie she killed but a shapeshifter. He tells her that Smith hit Laston Hennings Cyronics fifteen minutes before the FBI arrived. Olivia begins to feel that she has failed as William Bell had brought her all the way to another universe to tell her something so important.
Smith assembles the head with the omega symbol to a body. Suddenly the head and body attach, and his eyes open wide...