“The Fourth Horseman: Part 2” is episode eleven of season nine of Stargate SG-1.
At the end of the previous episode, “The Fourth Horseman: Part 1”, Gerak had converted to Origin and become a Prior of the Ori. The disease that had infected the SGC was rapidly spiralling out of control. Orlin was trying to come up with a cure, but there were two problems. The first was that the Ancient knowledge was killing him; the second being that he needed blood from a Prior.
Daniel and Mitchell have gone to meet the Sodan encountered in “Babylon” in order to capture the Prior. They also want to try and convince the Prior that the Ori are false gods. During this, they discover why the Ori have come. Teal’c and Bra’tac are intending to effectively cause a civil war amongst the Jaffa, in the hopes that this would cause Gerak and the High Council to cease supporting the Ori.
Bit of a deus ex machina ending.