The Fourth Horseman, Part 1

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

Synopsis
SG-6 returns to Earth from investigating a planet visited by a Prior, they inadvertently cause a plague that soon spreads beyond Stargate Command to the unsuspecting public. Orlin returns in the form of a child and tells the Tau'ri the truth about the Ori.

Previously on Stargate SG-1
The Priors attack several worlds including the Jaffa planets Kallana and Sartorus. Major General Henry Landry urges Gerak to continue to work together. The ascended Ancient Orlin follows Major Samantha Carter to Earth and falls in love with her.

Plot
Colonel Barnes and Lt. Fischer return from an undercover mission on P2X-885 that has fallen to the Ori.

Lt. Colonel Samantha Carter proposes creating a machine that will emit a field that will cancel out the powers of a Prior. She and Dr. Bill 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.

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 Lt. General George S. Hammond at an Air Force base he is taken captive and brought back to Stargate Command. 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 Henry Hayes 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 Lt. Colonel Cameron Mitchell and Dr. Daniel 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.

Notable Quotes
Landry: Colonel Carter! I've read your proposal.

Carter: And?

Landry: And, I'm not exactly sure what an aneurysm feels like, but I suspect I'm pretty close.

Lee: A couple of days?

Carter: Well, we'll just have to roll up our sleeves and burn some midnight oil if we have to.

Lee: "Midnight oil". Why didn't you just tell them we'd come up with a viable means of creating cold fusion while you're at it.

Carter: Sure, if you've got something.

Orlin: You're so close.

Carter: I know.

Orlin: Hello Sam. It's good to see you again. I've missed you.

Carter: Who are you?

Orlin: I had no choice but to take this form. It's me, Orlin.

Jackson: I'm sorry, aren't you breaking some major cosmic rules here? I mean, why did the Others let you go without wiping your memory clean?

Orlin: Honestly, I don't really know. I guess enough of them felt it was necessary for someone to step out of line and warn you.

Landry: I'm assuming you're talking about the Ori. We're already aware of the threat they pose.

Orlin: Believe me, you don't know everything. A long time ago, the Ori and the Alterans were one society—human—on an evolutionary path to ascension, but a philosophical division grew. The Ori grew more and more fervent in their religious belief. The Alterans... for lack of a better way of putting it... believed in science. The Ori tried to wipe them out.

Jackson: So instead of going to war, the Alterans built a ship, left their galaxy and came here. We know that both the Alterans and the Ori eventually ascended, and that the Ori passed on a religion called Origin to the next evolution of humans they created.

Orlin: Yes, but the central promise of the religion, everything Origin's followers devote themselves to, is a lie.

Landry: We're hoping that as long as you're here, you may be able to help us.

Orlin: I no longer possess the power to simply cure this plague as I could have as an ascended being. However, with the knowledge I still retain, I believe I can synthesize a cure using your medical technology.

Carter: You built a stargate in my basement with spare parts from a toaster.

Orlin: Actually, this'll be a little harder than that.

Carter: How's it going?

Orlin: Basically, I know what I need to make. I just don't have any of the right materials or tools.

Carter: This is the best we have. I can get you a toaster if you need it.

Orlin: Not unless you're hungry for toast.

Carter: Waffle iron?

In other languages

 * German (DVD/TV): Der Apokalyptische Reiter, Teil 1 (Horseman of the Apocalypse, Part 1) / Die Rückkehr von Orlin, Teil 1 (The Return of Orlin, Part 1)
 * Portuguese: O Quarto Cavaleiro, Parte 1 (The Fourth Horseman)
 * French: Le Quatrième Cavalier de l'Apocalypse - 1ère partie (The Fourth Horseman of the Apocalypse)
 * Italian: Virus Mortale (Parte 1) (Lethal Virus)
 * Spanish: El Cuarto Jinete (Parte 1) (The Fourth Horseman)
 * Czech: Čtvrtý jezdec apokalypsy (část 1.) (The Fourth Horseman of the Apocalypse)