Fringe: Season 2, Episode 17

2 - 17: Olivia. In the Lab. With the Revolver.

A woman dies from an advanced stage of cancer that she has not contracted. After more deaths, the team realize the victims were Cortexiphan subjects, and that the killer is transferring his own cancer to them to delay his own death. The murderer, James Heath, eventually tracks down Olivia and attempts to transfer the cancer onto her, but she fights back long enough for Peter to save her. Massive Dynamic puts Heath into a coma until they can work on his ability. Also, throughout the episode, Olivia ultimately decides not to tell Peter of his origin, but Walter believes it is time to tell him.