After David Robert Jones’ death and the closing of the Bridge between universes, his remaining shapeshifters were left abandoned and stranded on both sides. Hunted by Fringe Division, many of them took on desperate lives of petty crime, and the most resourceful of them somehow succeeded in punching through a new conduit between the universes, in hopes of smuggling valuable goods.
The intermittently existent tunnel beneath a parking garage could not be sealed with amber, and horrifically killed nearly every Fringe agent who was sent in… and a good number of unfortunate shapeshifters besides. Convinced her past dosing with cortexiphan offered her more protection, Olivia volunteered for the dangerous mission of tracking them. One got away, but she managed to get closer to the edge than anyone in Fringe Division had.
It was after this that she began having the nightmares.