When a perfectly healthy woman is found dead from a disease she never had, the Fringe team investigates the origin of this inexplicably fatal condition before it claims more innocent victims. Meanwhile, Olivia struggles to keep Walter's secret from Peter, and her loyalty to Peter is tested as time goes on. Guest Cast: Kevin Corrigan as Sam Weiss; Omar Metwally as Neil; Jaime Switch as Lloyd Becker; Curtis Caravaggio as Ken Messing.9 p.m. Thursday. Fox.