Walter and Olivia travel to the parallel universe, and the anticipated face-off between Walter Bishop and William Bell occurs.

After the extraordinary turn of events that shockingly left an imprisoned Olivia "over there," she fights to find her way home. Meanwhile, Peter and Walter try to move on with their lives unknowingly alongside alternate Olivia.

In the alternate universe, Olivia and the Fringe Division investigate weird accidents with casualties apparently with no connection except ballpoint pens found on the spots. But when Olivia sees the freak Milo, she suspects that he might be the responsible. Olivia and Charlie investigates and soon they follow a lead to a hospital where they learn what happened to Milo.

In the parallel universe, the Fringe Division investigates a case where a man was eaten from inside out by an extinct beetle. Meanwhile Broyles is considered missing and Lincoln is the head of the division. Olivia welcomes her boyfriend Frank that has just returned from Texas and wants to propose her. When a second man is also eaten by the insects, the Fringe Division identifies the scientist Dr. Armand Silva that was researching the cure for avian flu using this insect. Lincoln and Olivia goes to his address and split. Lincoln is locked in a refrigerating chamber while Olivia is brought to his laboratory, where she drinks water. Dr. Silva explains that only human beings are capable to host the beetle and a new cycle has just began. Olivia concludes that she has been infected by the insect and despairs.