The Fringe team is alerted to a case involving a passenger, Marshall Bowman (Neal Huff), that had transformed on a plane into a strange beast, due to a "designer virus" with which he had been injected.
Meanwhile, Olivia Dunham (Anna Torv), having accepted the replacement of her memories with those from Peter Bishop's (Joshua Jackson) original timeline, is assessed to be unfit for field work because she can't remember her "real" past, forgetting even family details.
Lincoln Lee (Seth Gabel) is put in charge of the Fringe team, though he is upset that Peter has won Olivia's heart over himself.
However, Astrid discovers that Conrad Moreau, the bio-terrorist Peter says was responsible for Bowman and Hicks' transformations in the original timeline, died five years previously.
Phillip Broyles (Lance Reddick) admits to Olivia that while she may be losing part of her memories, she is still considered an asset and is allowed back to active duty.
Marshall Bowman's sister, who had earlier claimed ignorance, is shown trying to motivate another man to inject the transformation formula.