Divide and Conquer

Divide and Conquer is the fifth episode of the fourth season of Stargate SG-1.

Plot
The episode begins with a meeting between Stargate Command personnel and the Tok'ra for the purpose of discussing a treaty summit. One of the SGC men, Major Graham, goes berserk and starts shooting up the place with a Goa'uld weapon. He kills several people and finally himself. The Tok'ra say that it is not Major Graham's fault. They inform the other summit attendees that Graham is a victim of Goa'uld mind-control technology - a Zatarc. This technology couldn't be proven to exist, until now. Nevertheless Freya/Anise says that she can detect any other Zatarcs that might be in SGC, thanks to a device she invented. However the device isn't without flaws.

Back at SGC Anise starts to check the SGC personnel (while the Tok'ra do the same on their base), beginning with Major Graham's team. She then finds out that Lieutenant Astor is also a Zatarc. Astor agrees to undergoe a procedure to remove the programming, but because it is very painful she demands it to stop and finally becomes violent. She breaks free and shoots at several people before she kills herself with a gunshot to the head.

Afterwards SG-1 is tested and they find out that Colonel O'Neill and Major Carter also seem to be Zatarcs. O'Neill and Carter are incarcerated, with the intention of sedating and restraining them during the summit. After being told that an autopsy of someone who has undergone the procedure might help to refine it, O'Neill agrees - he says Carter's brain is far more valuable than his. Carter gets injected with the sedative, and realises that she and O'Neill were lying, but not consciously. She asks for a moment alone with O'Neill, and says that there was something she and he were not admitting - "given their working relationship and military ranks." He understands her meaning and is then retested. He relates the incident as before, adding this time that he did not leave Carter on Apophis' ship because he cares about her "a lot more than I'm supposed to". Carter is retested, and like Colonel O'Neill she is also finally determined to not be a Zatarc.

However, they realize that Martouf could well be one. This conclusion proves to be true, and when the president appears, he starts to fire on him. However Carter manages to neutralise him with a Zat before anyone is hurt. His body is preserved in order to later be autopsied, and his death will contribute to anti-Zatarc knowledge for the Tok'ra.