Olivia Dunham (Anna Torv), suffering from a late-night migraine, runs across her fellow agent Lincoln Lee (Seth Gabel) at an all-night diner.
Meanwhile, Peter Bishop (Joshua Jackson), having been allowed to live on his own under guard, attempts to figure out how to use the Machine to return him to his original timeline.
Walter (John Noble) determines that the pigment from the man's skin has been extracted, and identifies traces of animal DNA along with human ones.
However, Fringe division learns that the baby, possibly still alive, was moved to a pharmaceutical company that was a subsidiary of Massive Dynamic.
As other incidents and deaths occur at a condominium high-rise, Walter deduces that U. Gene (Tobias Segal) is trying to extract the pigment from his victims to make himself visible, a treatment that will likely kill him if he continues the practice.
As Olivia reports U. Gene's death to Nina, she wonders if she herself, as a Cortexiphan nootropic drug trial subject, is unable to feel for others.
As she is getting ready to leave for the meeting, she is gassed, and agents working for Nina Sharp give her an injection, noting that once she wakes up, she won't remember the last two hours, but she will have "one hell of a headache".
"Wallflower" was co-written by former script coordinator Justin Doble and story editor Matt Pitts, while Treme and The Wire veteran, Anthony Hemingway, directed.
He loved Walter's experiment with the mice and the maze, and believed the death of Eugene Bryant was "one of the most poignant moments Fringe has ever produced.