While Olivia copes with migraines, she and her team investigate an invisible force which kills its victims and causes the body to turn a ghostly white. As they trace the pattern of deaths, the Fringe team realizes that the force is linked to someone who died of an unknown genetic disorder.
This episode's glyphs spell:
See the glyphs explanation for S4E08 - Back to Where You've Never Been.
The Observer can be seen in the crowd outside of the building where the agents are searching for Eugene Bryant.
A brochure for "Octopus Insurance" can be seen in the Green's home in 'And Those We've Left Behind', foreshadowing Eugene Bryant's chromatophoric, pigment-altering abilities in 'Wallflower'.
The ParkView Hospital logo in 'Wallflower' foreshadows the return of Walter's universe portal in 'Back to Where You've Never Been'.