“This Mortal Coil” is episode ten of season four of Stargate: Atlantis.
The city’s stargate is not working, something that happened after Dr. McKay was trying to improve it. Whilst trying to fix it, something hits the city, and McKay is convinced it is a probe for the human form Replicators.
McKay is convinced that there were nannites in the probe and that some people are acting differently, and he is not the only one who has noticed it. People who are also healing unnaturally quickly. It turns out that everyone but Teyla, Rodney, Ronon and Sheppard is apparently not alive.
They are not on Atlantis though, and they are not actually the real people.
Elizabeth Weir makes a return visit in the episode, although she is also a copy, as the real Weir was killed several months ago in “Lifeline”.
This episode shows the truth of the vision of the destruction of Atlantis seen in “The Seer”.