Double Jeopardy

"Double Jeopardy" is the twenty first episode of the fourth season of Stargate SG-1.

Synopsis
SG-1 arrives on Juna, where they are captured by Cronus' forces, where Cronus himself doesn't take the reunion well. However, unknown to him, SG-1 is actually the robot copies from the real SG-1's encounter on Altair three years ago.

Plot
On the world Juna, the Stargate activates and SG-1 comes through. However they are soon attacked by Jaffa and the natives of Juna. One of the natives named Darian recognizes them and asks them how they dare to return. SG-1 is captured but Colonel Jack O'Neill escapes. Major Samantha Carter, Dr. Daniel Jackson, and Teal'c are brought to a pyramid and confronted by Sindar, the First Prime of Cronus. SG-1 is then imprisoned and discuss what to do next.

In the evening Darian goes home but finds O'Neill waiting for him. O'Neill asks him what has happened on this world. Darian explains that SG-1 helped them free their world from Heru'ur but then Cronus came and enslaved them again. He also tells the Colonel that this time he won’t believe them. O'Neill leaves.

The next day Cronus appears and the prisoners are brought before him. O'Neill sneaks in the base, disguised as a warrior of Juna, and has to watch as Cronus orders Darian to kill Daniel with a Staff weapon. Darian is at first reluctant, but obeys when the Jaffa hold their weapons on his people. The shot blasts Daniel's head from his shoulders only to reveal that he is in fact a robot, much to the shock of the Juna and Cronus. Cronus sends the natives of Juna away and commands Carter and Teal'c to tell him what they are. They don't answer, and so are sent to Cronus' Ha'tak to be questioned. Darian goes home and tells his wife what has happened.

At Stargate Command the Gate is activated and they are contacted by Harlan, who they then let in. He tells them that they should help their robot doubles (from "Tin Man") who have started to go on missions and now are missing. Both Major General George S. Hammond and Colonel Jack O'Neill are reluctant about rescuing the doubles. Harlan then shows them the coordinates of the world and they remember having visited it previously. They dial the Gate, send a MALP through and see the robot O'Neill, who has overcome the Gate's Jaffa guards. Shortly thereafter Darian arrives and they explain the situation. SG-1 (without Dr. Daniel Jackson) then goes through the gate to help. The two O'Neills' get into an argument, which devolves into the beginnings of a wrestling match, but eventually they agree to work together.

On the ship a Goa'uld named Ja'din questions the robot Carter and Teal'c, but they refuse to answer. She then tells Cronus that Teal'c wants to speak with him and he agrees. Teal'c is brought to Cronus but he kills the Jaffa and attacks Cronus. However before he can kill the System Lord a Jaffa frees his master. The female Goa'uld again questions Carter and she tells her how to reactivate the energy source of the destroyed Daniel. This turns out to be a self-destruct command as well. The "dead" robot explodes, killing the Goa'uld and freeing Carter.

In Darian's home, SG-1 and their remaining doubles make a plan to free the others and kill Cronus. Later a Jaffa brings O'Neill in the pyramid but are ambushed by Darian, SG-1, and the doubles, who kill the Jaffa. The robot O'Neill is critically damaged in the firefight. The team is then beamed on board by the robot Carter. Teal'c helps his double but he is also overwhelmed. Before Cronus can kill him (in the same way as he killed his father Ronac, by crushing his symbiote) he is shot by the robot Teal'c, who then dies, his last words being "For our father". In another section of the ship, the robot Carter accesses the ship's controls through a powerful forcefield, cutting off all sections, but fatally damaging herself as well.

Darian attempts to help robot O'Neill as best he can, although the double tells him not to bother. Darian knows enough that as a machine, he could be repaired, but robot O'Neill reveals that he is running out of power and any repairs would come too late for him. In the end O'Neill beams down to the pyramid and tells Darian that Cronus is dead. He informs his counterpart that SG-1 is fine, but the copies went down in the line of duty. Robot O'Neill asks him that despite their origins, in the end are they really all that different, and O'Neill agrees that they aren't. He watches as his double finally dies. Afterwards SG-1 secures Cronus' ship for themselves.