Genre: Mystery

Walter explains to Olivia how Peter came from the alternate universe, and how he was willing to risk everything to save his son.

The arrival of a building from the alternate Earth causes massive death and destruction to those occupying the site at its arrival. Walter soon realizes that to equalize the balance between universes, another building will have to disappear… along with everyone inside it. The team's only chance is for Walter to activate Olivia's long-buried ability to distinguish objects from the other universe.

When all of the groom's relatives asphyxiate at a wedding, the Fringe division investigates and quickly ascertain that a human agency is responsible. Walter realizes that the formula for the toxin was based on research conducted by his father, Robert Bischoff, and that the killer isn't stopping with a single test of his lethal concoction.

A Dutch industrial consultant arrives for an appointment and dies in a painful explosion of blood. Olivia and Peter arrive on the scene first and discover that the blood contains a pathogen and everyone in the building may be contaminated. While Walter and Astrid work outside the quarantined building to create a cure, the virus develops unique characteristics that pose a danger to the entire world.