Gemini

"Gemini" is the eleventh episode of the eighth season of Stargate SG-1.

Synopsis
SG-1 is shocked to see a duplicate of Lt. Colonel Samantha Carter, who reveals that she is a Replicator created by Fifth. She wishes to be destroyed with the Replicator disruptor, to prevent Fifth from getting his hands on her again, since he is heading straight for the Milky Way. However, the Tau'ri plan to have her help them defeat them, since she claims Fifth has created a cipher to become immune to the disruptor.

Previously on Stargate SG-1
SG-1 encounter a group of Human-form Replicators on the planet Hala. They managed to trap them in a Time dilation field by betraying the trust of Fifth. A year later, Major Samantha Carter is beamed to a Replicator ship and tortured by Fifth before being rescued by SG-1. Fifth then creates Replicator Carter.

Plot
Stargate Command receives an unscheduled off world activation, and with it an old IDC that had been used by Lt. Colonel Samantha Carter. Then comes the message, "SEND M.A.L.P.," and when one is sent through, it reveals a second Carter. She identifies herself as a Human-form Replicator, designed by Fifth with all of Carter's memories and thoughts. Her message is urgent: Fifth has discovered a way to overcome the Replicator disruptor Brigadier General Jack O'Neill designed while he had the Ancient database downloaded into his brain. The replicator version of Carter has rebelled against Fifth and offers her assistance in altering the weapon to work again.

Carter accepts the proposal, and with O'Neill's approval, goes to the Alpha Site with Teal'c to work on the weapon. After connecting to the Replicator collective, Replicator Carter downloaded the cipher. After experimenting with the disruptor, they adjust the weapon and launch a Replicator disruptor satellite.

However, it is eventually revealed that Fifth had no immunity to the weapon, and in fact he had sent her to study the weapon and develop the very cipher she claimed to be trying to defeat. She destroys Fifth with the disruptor satellite that had worked all along and makes her way to the Stargate. After taking out the guards, she begins dialing the Stargate. Teal'c attempts to stop her but she deactivates the nanites in the arm Teal'c is holding and she escapes.

Notable Quotes
O'Neill: Alright, you got our attention. Who are you?

Replicator Carter: My name is Samantha Carter.

O'Neill: Alright. We've got a little conflict with that statement. We've already got one here.

Replicator Carter: There are two of us.

O'Neill: If only.

Replicator Carter: I was made in Samantha Carter's image. I know what she knows. Feel what she feels.

Carter: You were made. Who made you?

Replicator Carter: The one you call Fifth.

Carter: Oh my god. She's a replicator.

Carter: ...and we need the Asgard to send us a disruptor satellite as soon as possible.

O'Neill: I've already talked to 'em. Be there in there in 30 minutes, or it's free.

O'Neill: I need you to be perfectly honest with me. Is Carter letting herself get too involved in this one?

Teal'c: Colonel Carter and the replicator share thoughts and memories. It is understandable that a certain sympathy would develop between them.

O'Neill: Can’t have that.

Teal'c: However I do not believe Colonel Carter would allow these feelings to interfere with the commission of her duties.

O'Neill: Fair enough. But when the time comes, I want you to finish the job.

Teal'c: Understood.

Fifth: Why?

Replicator Carter: You should know. You made me what I am.

Carter: We will stop you.

Replicator Carter: You're forgetting, I know exactly how your mind works. I know what you're going to do before you even think of it.

Carter: The fact is, she learned betrayal from Fifth. And he learned it from me.

Goofs

 * Replicator Carter claims to be able to upload data directly into the base's mainframe, and then moves her hand into a computer monitor, presumably to allow her nanites to interface directly with the computer. This does not make sense considering that monitors only display output from a computer and are not capable of inputting data into a computer. Later in the episode she interfaces with a computer by moving her hand into a keyboard, which makes considerably more sense, since keyboards are input devices and so interfacing with it would allow her to interact with the computer. (It should also be noted that modern monitors are capable of two-way signaling.)
 * After Replicator Carter contacts Stargate Command and Brigadier General Jack O'Neill orders MSgt. Walter Harriman to deactivate the gate he presses the Iris deactivation button.

Death

 * Fifth

In other languages

 * French: Vulnérable (Vulnerable)
 * Italian: Gemelle (Twin)
 * Spanish: Géminis (Gemini)
 * Czech: Blíženci (Gemini)
 * German: Gemini (Gemini)
 * Hungarian: Ikrek (Gemini)