“Foothold” is episode fourteen of season three of Stargate SG-1.
SG-1 return from a mission looking for Sha’re’s child to the SGC. A chemical rupture has apparently sealed off an entire level, but the team are sedated whilst supposedly being treated after their mission. Teal’c comes around earlier than the rest, due to his symbiote, and sees some aliens who are planning an invasion, as well as the normal SGC personnel who appear to be cooperating. With Teal’c regaining consciousness, he is able to escape and then go and free Carter.
The people who look like members of the SGC are, of course, disguised aliens, who are seeking to establish a ‘foothold’ on Earth. The ever-popular Colonel Maybourne gets involved.
Things get confusing when Teal’c is told that he and Carter are actually hallucinating and suffering from paranoid delusions thanks to the effects of the chemical spill. Which keeps you guessing.
Looks like they ran out of money for the CGI Goa’uld larvae – they’ve gone back to using the real puppet thing. Which looks a bit unconvincing now.