McKay and Mrs. Miller

"McKay and Mrs. Miller" is the eighth episode of the third season of Stargate Atlantis.

Plot
Jeannie, McKay's sister, is seen playing with her daughter Madison. While watching her daughter push a toy train across a bridge, Jeannie is suddenly hit with a moment of inspiration, and begins writing down mathematical formulas using fingerpaint and Madison's easel. She submits her work, and catches the eye of the US Government, more specifically, the Stargate Program. The next thing she knows, Jeannie is approached by Colonel Carter with an offer to work for the SGC.

Jeannie, however, refuses to work for the US Government because she believes her physics calculations serve no practical purpose and vehemently opposes the commercial exploitation of theoretical science. McKay is brought back to Earth in an effort to convince his sister to work for the SGC. McKay visits Jeannie and her husband (Caleb) and daughter. They don't really know what to think of him, and McKay and his sister bicker about the past. Rodney wants her to come with him and help out for a few months because she's almost as brilliant as he is and would be a great help to the Stargate Program. Jeannie balks until McKay beams her aboard the Daedalus. McKay then reveals that Jeannie's calculations can help solve the problems that plagued Project Arcturus. Instead of trying to draw zero point energy from our own universe and release hazardous exotic particles, McKay plans to draw energy from a parallel universe via a matter bridge so the exotic particles would be vented into the hopefully uninhabited parallel universe instead. Working together, McKay and Jeannie managed to resurrect Project Arcturus and successfully activate it without releasing exotic particles. While being tested, a foreign object suddenly materializes inside the containment chamber. When the scientists arrive to investigate, they are shocked to discover McKay, or an alternate version of him. The alternate McKay demands to see the person in charge of the project – McKay.

Meanwhile, the friction and differences between McKay and Jeannie becomes more evident as their bickering and sibling rivalry become more intense. Matters aren't helped when they first meet the alternate McKay. Alternate McKay explains to the Atlantis team that he was sent to this universe in order to warn them that his universe is slowly being destroyed by the exotic particles being created by Project Arcturus. The project is immediately shut down to prevent any more damage. However, the alternate McKay admits that the trip through the matter bridge is one-way only, so he will be staying in Atlantis permanently.

Already, there are major contrasts between McKay and alternate McKay, who is soon called "Rod". Rod is more outgoing and social than McKay, and is more comfortable in engaging with personal relationships. Much to McKay's dismay, Rod quickly befriends most of the Atlantis team, including Jeannie. McKay slowly realizes to his horror that he is actually jealous of Rod and his ability to socialize, as well as being able to get along well with Jeannie. Meanwhile, more problems begin to arise. Even though Project Arcturus had been shut down, the matter bridge is still open and Rod's universe is still being destroyed. The Atlantis team in Rod's universe devises a way to stop the process but it would involve destroying Rodney's.

Suddenly, McKay realizes that there is an alternate way to close the matter bridge without having to destroy either universe. The plan involves using massive amounts of energy to forcibly close the matter bridge. Unfortunately, they only have one energy source powerful enough to use, the ZPM. While preparations are being made, Rod approaches McKay, telling him that he is going to attempt to beam himself back through the matter bridge and return to his own universe. McKay tries to dissuade Rod, pointing out that everybody in Atlantis likes him. Rod however is adamant, stating that even though his teammates in his universe have their faults, they are still his team. Rod even admits that he is slightly jealous of McKay's self-confidence in his own talents and ability to say what is on his mind without hesitation.

The plan continues, and the alternate McKay begins to draw energy from the ZPM to close the matter bridge. They successfully close the bridge, but McKay keeps the energy running in order to give Rod time to beam back to his own universe. Once the power is cut however, McKay realizes in horror that the ZPM has been drained of all power as Atlantis is plunged into darkness.

With her job done, Jeannie begins to pack up and prepare to return to Earth. McKay comes to see her one last time, and the siblings reconcile their differences. After a tearful farewell, McKay goes to the mess hall, where he finds Sheppard, Teyla, and Ronon just hanging out, talking and joking with each other. McKay joins them, and is surprised as his teammates admit that they didn't quite like Rod all that much, stating that he was "creepy". They also wonder if Rod ever made it back to his own universe. Then, in a surprising move, McKay begins to hang out with the trio, talking and joking along with them.

Trivia

 * Jeannie Miller is portrayed by Kate Hewlett, who is the real-life sister of David Hewlett, who plays Rodney Mckay on the show.