Ripple Effect

"Ripple Effect" is the thirteenth episode of the ninth season of Stargate SG-1.

Plot
An unscheduled offworld activation has summoned General Landry and Dr. Lam to the control room. As the Stargate prepares to open, there is a brief, blinding flash of light and an odd noise. SG-1, dressed in their black uniforms, comes through the gate. Landry notes that they are early.

A briefing follows, during which a number of discrepancies come to light. Before they can be resolved, there is an offworld activation. SG-1 (in green uniforms) arrives right on schedule. Landry orders Lam to investigate. They conclude that both teams are really SG-1, but that the facts indicate that the green SG-1 is ours. (The black team, for example, believes that the Tok'ra Selmak is still alive.) Back in the conference room, Landry and the green team discuss the situation.

In need of more information, a series of interviews takes place. Black team Jackson is interviewed by green team Mitchell; Landry speaks with the black team Mitchell; green team Jackson takes notes in his discussion with the black team Teal'c. Meanwhile, green team Carter and black team Carter talk science as they try to sort out what caused this problem.

As the green team Carter briefs Landry and the rest of the green team SG-1 -- she suggests the beachhead black hole the Ori tried to create is involved in bringing another SG-1 here from a parallel universe -- there is another unscheduled offworld activation. Assembled in the control room, the green team and Landry watch as another SG-1 team, taking fire and dressed in blue tiger camo, rush through the gate. Landry orders all gate travel restricted.

While Dr. Lee discusses the situation with the green team Carter, the black team Carter joins them. As they work, more SG-1 teams arrive. Eventually, Landry takes the green team Jackson and Teal'c to a room where Dr. Janet Fraiser awaits them. They are stunned, as our universe's Fraiser was killed two years ago. She reveals that her Earth is suffering from the Ori plague. Also on this team is Martouf, who Landry takes to see the green team Carter, now working on the problem with at least 16 other Carters. As green team Carter sits talking to Martouf -- who she was forced to kill several years ago, black team Carter approaches and delineates the problem and a potential solution.

The green SG-1 and Landry confer with Kvasir, who comes in Thor's place, about a risky plan that involves using Prometheus to close the breach in space that has diverted so many SG-1 teams. Unfortunately, all of the teams will then be stranded permanently.

Fraiser visits Landry to ask for more time to find a better solution. Sympathetic, Landry feels, however, that he must act first and foremost to protect his own reality.

Staffed only by the green and black SG-1s, the Prometheus heads off. But the black team soon launches a plot to take command of the ship by breaking into the armory. Armed with zats, they capture the green team Mitchell and take him to the bridge just as the Prometheus is in position to launch its Asgard-primed weapon to close the breach.

The green team is taken to a brig while the black team re-routes the Prometheus to Atlantis in the Pegasus Galaxy. Their intent is to steal Atlantis' ZPM and drop off the green team on a habitable planet. As soon as Teal'c destroys the camera in the cell, the green team hatches a counterplot.

Green team Mitchell asks to speak with the black team Mitchell. The black team feels that the Atlantis Z.P.M. is only used to power the Stargate for one-way travel to the Pegasus Galaxy. They need the Z.P.M. to power the Ancients' Antarctic weapon, suggesting they do not fully understand the situation on Atlantis and the need for the Z.P.M. to cloak the city from the Wraith. Green team Mitchell realizes that the black team created the entire situation to come to our universe deliberately -- and that they already have a way home.

Once the green team Mitchell is back in the cell with the green team, Carter hotwires the door and she and Jackson set off for the engine room, while Mitchell and Teal'c head for an armory. As they try to open the armory door, the black team Jackson and black team Teal'c show up and prepare to take green team Teal'c captive once more. It's a trap: the green team Mitchell is really the black team Mitchell.

But before they can touch Teal'c, green team Carter and green team Jackson arrive and zat black team Jackson and Teal'c. Our SG-1 anticipated the trap from their other selves, and set one of their own. The black team is taken to a holding cell where the door cannot be hotwired; black team Mitchell is dressed only in T-shirt, underwear and boots. Green team Mitchell, similarly clad, locks the door on them.

Green team Carter works out a plan for returning the many SG-1s to their respective universes, and upon the return of the Prometheus to Earth orbit she requests the use of an Asgard weapon. They fire it into the open Stargate, recreating the conditions the black team used to cause the breach.

Starting with the black team, the teams are sent back to their realities. On the ramp, the black team Mitchell stops and enigmatically tells the green team Mitchell that, when the time comes, "Cut the green one."

Finally, the last team assembles. After Carter, Jackson, and Teal'c share an emotional goodbye with Martouf and Janet, Landry provides them with the cure to the Ori plague and the team heads home to save its Earth.