Fringe/Recap/S02 E17

Season 2, Episode 17:

Olivia. In the Lab. With the Revolver.
The Fringe team investigate when people start turning up with strange cancerous growths. They discover that another cortexiphan subject is using his ability to transfer his own illness to other people. During the investigation, Olivia meets with Sam Weiss and he helps her decide whether or not to tell Peter about his origins: in the end, she elects to keep the secret.