A woman is hit by a bus, which is the result of a chain of events set off by a strange man.
Olivia begins/returns to work at the Division on the Other Side.
Walternate tells Broyles that he wants our Olivia because of her ability to cross between worlds. If her new identity doesn't hold, she will no longer be necessary.
More people die by being hit by a bus. The probability of this happening so many times is practically impossible, so the Division is called in to investigate.
Agent Lee joins the investigation and notices an obsolete ballpoint pen on the floor. He speculates that maybe the pen started a chain reaction leading to the death.
During the investigation, Olivia sees a vision of Peter.
Agent Lee finds another ballpoint pen at a different bus accident. Astrid determines the odds are 0.00 that a pen could set off a chain of events that would cause a bus accident and death.
The Division is called to yet another accident and Olivia spots the man responsible. He manages to escape by jumping off the bridge onto an oncoming truck.
The man, Milo, goes home to his sister who tells him he has to “follow their rules” and that he is “overreaching”.
Olivia obtains a link to Bryant Hospital. At the hospital, they notice the patients using ballpoint pens. The lead doctor also identifies all the bus accident victims.
They are also able to positively identify Milo from video and the doctor tells the Division they treated him to increase his IQ, from a severe cognitive disability.
After the drug trials, the doctors regress their test subjects. Milo does not want to return to his previous state, so he has been murdering all the people involved in the trials.
At the hospital, Olivia has a vision of Walter.
Olivia and Charlie go to question Milo’s sister. She gives them a goodbye note Milo has written her, with an address where they can find him.
Olivia and Charlie head to the Patricia Hotel, where Milo is waiting and planning Olivia’s death.
Olivia sees Milo and chases him down a back alley. But things don’t go exactly as Milo has planned. Right where Olivia should need oxygen, she doesn’t remember to pause and take a breath. This delays Olivia a few seconds and spares her life. She doesn’t remember needing oxygen because she is not from their world.
The drugs were not able to be removed from Milo. He now is lost in another state, only able to communicate with computers.
Walternate visits Brandon, the scientist trying to figure out how Olivia can cross over. So far, all the test subjects are feeling a high level of anxiety causing their readings to fluctuate. Walternate suggests submerging the subject in a water sensory deprivation tank.
At the end of the episode Olivia has a vision of Peter, reminding her of who she really is.
Peter: You know what you didn't die today? Because you didn't know the protocol. If you stopped for oxygen you'd be dead right now. But you did something he couldn't factor in, you kept running. You know why you did that. It's the same reason you thought you saw Walter in that hospital. It's the same reason you think you are seeing me now. You're not from this world Olivia. You're not her.
Olivia: You're not real.
Peter: Real is just a matter of perception. I am here and I'm a part of you, that you have to hold on to. You can't forget who you are Olivia. You can't forget where you're from.
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Brandon: Do you miss it?
Walternate: Miss what?
Brandon: Being a scientist?
Walternate: I'm still a scientist Brandon; I just have a much larger laboratory.
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