The Fourth Horseman (Part 2)

While Orlin is working on a cure for the Prior plague, Mitchell and Daniel capture a Prior offworld to further the research of the antidote. Teal'c tries to stop Gerak, now a Prior, from corrupting the entire Jaffa Council towards Origin. Teal'c ultimately convinces Gerak to switch sides and he cures the SGC of the plague, but it costs him his life. Thanks to Gerak's efforts and Orlin's work, a cure is found for everyone else, but Orlin now has brain damage and no memory of who he is and is put in a mental hospital.