The Fourth Horseman, Part 1

The Fourth Horseman is the tenth episode of the ninth season of Stargate SG-1.

Plot
Colonel Barnes and Lieutenant Fisher return from an undercover mission to another planet that has fallen to the Ori.

Colonel Samantha Carter proposes creating a machine that will emit a field that will cancel out the powers of a Prior. She and Dr. Lee begin to work on the machine.

Gerak is visited by a Prior on Dakara. He tells him that he has read in the Book of Origin, and he becomes convinced that the Ori are the gods they've been searching for. He sets out to make all Jaffa bow to the Ori as gods. Gerak then presents his beliefs to the Jaffa High Council and several of them are interested. Teal'c and Bra'tac discuss this after the meeting and they decide to oppose Gerak's vision. However after some time the council agrees to legislate Origin.

Lieutenant Fisher returns to Earth as a carrier of the Prior Plague, which appears to be both airborne and persistent. When he listens to a speech of General Hammond at an Air Force base he is taken captive and brought back to SGC. At the base he reveals that he was 'blessed' by a Prior during a Prostration, who seemingly was aware that he was from Earth. Also because he is the carrier of the plague he isn't sick. However the plague begins to spread wildly throughout the country, until the President of the United States is forced to put the entire nation under quarantine.

While Carter is still working on the device, a young boy suddenly appears. It's Orlin, an Ancient who returned to make some startling revelations about the Ori and their true intentions. He reveals that the Ori won't give the secret of Ascension to their followers. Instead they suck the life force from them which gives them more power. Not wanting the Ori to gain control of the Milky Way Galaxy, he descended yet again to help Carter find a cure.

Orlin then starts to work on a cure but during a lunch (where he also reveals that he still has feelings for Carter) it becomes clear that he starts to lose what is left from his ancient knowledge. However he finds out that that they will need the blood of the Prior who infected patient zero. Capturing him may be more difficult than anything SG-1 has ever done before. However the weapon of Carter and Lee is finally completed and thus Col. Mitchell and Jackson lead a team to capture the Prior.

On Dakara a Prior visits Gerak and tells him to go to Chulak to convert the population to Origin and he agrees to do so. However in the end he can't bring himself to follow the order. The Prior is angry and thus takes him to Celestis to meet the Doci. There, he is turned into a Prior of the Ori and returns more powerful than ever.

In other languages

 * German: Die Rückkehr von Orlin Teil 1