Police Officer Gillespie receives a phone call telling him "It's time." He is instructed to go to a metro station and take a black briefcase from a man wearing a black trench coat. Gillespie arrives at the station and locates the man. Gillespie grabs the suitcase and his body begins to crystallize before suddenly exploding!
Meanwhile, Olivia meets with Sam Weiss in her continued efforts to recover from her accident. He begins to ask her if she is having trouble sleeping and if her headaches have started yet -- what headaches?
Back at the lab, Peter begins to review apartment listings with Walter who is reluctant to move. Astrid interrupts them when she discovers an article in their database concerning the explosion at the metro station in Philadelphia. No bomb residue was found at the site arising suspicion among our team. They head to Philadelphia to investigate.
Our team arrives at the site. They discover that no antiterrorism bomb sensors or disabling devices picked up the bomb. The video cameras also received magnetic static causing most of the images to be wiped at the time of the explosion. As Walter finds crystal shrapnel from the bomb in one of the victims' bodies, Peter discovers Gillespie's badge wedged in a bench, but no police officers were found among the victims. Walter finds a crystallized ear, and they conclude that Gillespie was a human bomb.
At the lab, Walter and Astrid piece together Gillespie's crystallized body. They find needle marks in between his toes. The serum appears to have caused the water in his cells to solidify and emit a massive amount of energy.
Olivia and Peter interview Gillespie's wife for more information. Olivia suddenly begins to feel sick and has flashes of memories from the parallel universe. She rushes to the restroom where she discovers viles of serum and needles that Gillespie had used behind a loose tile.
A fellow member of Gillespie's unit, Diane Burgess, gets up in the middle of the night and injects herself with similar serum to that that was found in Gillespie's home. The next day she is approached by Colonel Raymond Gordon. He tells her she has been called back into duty and that she must fly to DC on Friday. He also informs her that "Tin Man Perimeters" are in effect.
Olivia returns to Sam Weis as her headaches have begun. He informs her that she is suffering from acute nominal aphasia - part of her brain has been asleep and once it wakes up her memories will come rushing back.
Walter has concluded that Gillespie had been injecting himself for at least a year due to the amount of serum in his body and his body's metabolism rate. This means that he began injecting himself while still serving in Iraq.
Astrid pulls up Gillespie's file. His unit was exposed to the deadly chemical cyanogen chloride. He was also part of a classified experimental project called Operation Tin Man, which was shut down shortly after he returned home. Doctors are also listed on the project but it would take to long to go through proper channels to locate and talk to them. Peter decides to use his contacts in Iraq to get to the doctors before the next tragedy occurs.
Peter's informant leads him to one of the doctor's involved in the project. He discloses that they developed the serum to neutralize the cyanogen chloride that the soldiers had been exposed to. Only a few survived, and they discovered that there was an unintentional byproduct as the buildup in human tissue turned people into bombs. Colonel Gordon tried to save the program before it was shut down.
Meanwhile, Walter tests a theory that radio waves set off Gillespie after he crystallized by injecting a watermelon with the serum. After turning on the radio waves, the watermelon suddenly explodes.
Broyles has learned that a bomb will be detonating in DC today. Three of the four test subjects in Operation Tin Man have been accounted for leaving Dianne Burgess as the only one not accounted for. They believe she does not know that she is being used as a bomb. Colonel Gordon is responsible for controlling the signal to detonate.
Broyles locates Burgess in a cab heading to the metro station. The Fringe team arrives on the scene to try to jam the signal. Walter determines that they must wait until she is inside the station in order to triangulate Gordon's location. Burgess enters the station and receives a phone call from Gordon. He orders her to take a black briefcase from a man in a black trench coat. She spots the man and begins to head towards them as our team tries to jam the signal. They are unsuccessful leaving Olivia and Peter inside to fend for themselves. Burgess takes the briefcase and begins to crystallize to her horror. Peter spots Gordon and knocks him down as Olivia smashes the transmitter device saving Burgess' life as she begins to decrystalize.
Olivia returns to Sam who merely measures her hand before sending her home. This enrages Olivia who walks over to him and puts a gun to his head. Her hand, however, is rock steady, and she has managed to walk on her own...free from her cane at last.
At the lab, Broyles interrogates Gordon who warns that the enemy is amongst us and the end is coming. He tells Broyles that the enemy is here collecting data and making observations. That is what was in the briefcase. They are studying our sciences and our technology to use against us. Gordon doesn't know who they are but he warns that we will find out but by then it will be too late...