User:MeekSaffron/FH

SG-1 returns from a very rainy planet. O'Neill wants to clean up first, but Hammond orders them to the infirmary. Teal'c is a bit on guard about their security escort (Sgt. Warren), who declares he's just a precaution due to a chemical spill on Level 23, but nothing else seems awry. Until Dr. Fraiser sedates the team and says "Let's begin."

Teal'c awakens later in the infirmary and overhears Fraiser and Hammond speak with unfamiliar aliens of a procedure which failed to work on him and Carter, but that's acceptable while they continue to invade Earth as a possible new homeworld. He feigns unconsciousness and overpowers Siler, Warren and Carter's escort. Carter awakens, and Teal'c fills her in. As their escape is detected, Teal'c vows to keep the imposters busy while Carter departs Cheyenne Mountain to summon reinforcements.

Carter informs Colonel Maybourne of the Foothold situation. However, when she arrives at the café where she told Maybourne to meet her at, he tells her he believes Hammond's story over Carter's paranoid delusions. "Maybourne, you are an idiot every day of the week! Why couldn't you have just taken one day off?"

O'Neill and Daniel arrive and don't behave like pod people. O'Neill mispronounces tetrachloroethylene, which Carter confirms can cause hallucinations. Maybourne orders her to return to the SGC, O'Neill and Daniel say she's free to walk away, Carter is wary but weary. She agrees to return with Maybourne and, perhaps, her friends.

Dr. Frasier quickly disabuses the viewer of that notion when she drops the act with Teal'c, saying they may begin experimenting immediately. On Maybourne's private plane, Carter observes O'Neill's image flickered to an alien for a second, and kills him and Major Davis when they attack, revealing their full alien forms upon death. She places a small disc (later called a mimic device) attached to "Daniel's" chest to herself, taking on Daniel's image though without access to his mannerisms.

The real Jack O'Neill and Major Davis wake up, hanging from an SGC ceiling in organic-looking harnesses. Others, including General Hammond and Dr. Frasier, are suspended alongside them, unconscious. Dr. Frasier's evil twin helpfully walks in and gives the CliffNotes version, scanning an SGC member, imparting his thoughts and appearance to an alien. O'Neill and Davis free themselves, so O'Neill tries to disconnect the real Frasier. An alarm sounds instead and he knocks out Frasier's duplicate, reflecting on the weird experience.

Daniel walks in, not sounding even like the fake Daniel earlier, but fortunately it's Carter with a mimic device. She informs them that Maybourne's forces are going to storm this facility in 29 minutes, so they have to find a way to disrupt the disguise and disconnect their people. Carter duplicates and broadcasts the noise the plane engine was making at a certain altitude, demasking all the aliens. With this obstacle and Maybourne securing Cheyenne Mountain, the aliens flee through the Stargate. Carter realizes they can't permit aliens who have had access to everyone's minds leave, but many escape before she's able to shut down the gate. The rest self-destruct.

All remaining personnel awoke as soon as the aliens left or self-destructed. Hammond orders Carter's procedure be performed on all future incoming travellers and all their codes changed. Maybourne, Hammond and SG-1 have a rare moment of mutual respect for his role in retaking the facility.

Trivia

 * An alien foothold of the SGC is a key part of "Proving Ground", and the mimic devices appear again in "Smoke & Mirrors".
 * Continuing storyline: In the beginning of the episode, SG-1 discusses the Harcesis child, a key component of the season three episodes "Forever In A Day", "The Devil You Know" and "Maternal Instinct".
 * Carter leaves Cheyenne Mountain through what appears to be the same shaft that Colonel Cromwell used to gain entry in "A Matter of Time". She justifies the low security at this shaft to the viewer as "The base was designed to keep people out, not in", and the Mountain was experincing time dilation in the other episode.
 * Maybourne's private plane is likely the same one that the real O'Neill flies with him in "Shades of Grey".