Agent Lincoln Lee (Seth Gabel), following both the death of his long-time partner by a shapeshifter, and the recent changes in Olivia Dunham's (Anna Torv) memories that have made her forget her romantic meetings with him, struggles to find his place in the Fringe division.
With the main Fringe team preparing to take Gene, Walter Bishop's (John Noble) cow, for "grazing day", Agent Lee offers to take case dockets through the dimensional bridge to the parallel universe to allow Astrid Farnsworth (Jasika Nicole) time to spend with her father.
Once through, however, Olivia's doppelganger, Fauxlivia (Torv), states that the dockets will have to wait as there is a new Fringe case on their side; Agent Lee offers to help.
In one such region, two workers discover nearly two dozen bodies in various states of decay in a church, and these are quickly identified as the missing criminals.
The Fringe division discover telltale signs of shapeshifter extraction marks, though more advanced than the means used by the initial models created by Walternate (Walter's doppelganger).
Unknown to the rest of Fringe, Broyles contacts the Nina Sharp (Blair Brown) of the parallel universe, who arranges for a sniper near the building where Canaan is being held.
Agent Lee takes Canaan across the bridge back to the prime universe, where Walter and Peter Bishop (Joshua Jackson) promise to help study and fix him.
He goes on to explain the concept—a billionaire playboy dressing up in a cape to fight crime—and the alternate Fringe agents conclude that their equivalent is a character called M.a.n.t.i.s.