Old friends return as the Replicator story arc takes a massive leap forward in “Ghost In the Machine,” the fifth episode of Stargate Atlantis‘s upcoming fifth season.

The Replicators were last seen in the Season Four episode “Be All My Sins Remember’d,” which ended with a startling revelation: though the Replicators in the Pegasus Galaxy were believed to be destroyed, in fact a rebel group of the technological foe survived and is under the leadership of Elizabeth Weir, the former head of the Atlantis expedition — or some form of her.

Today GateWorld received some scattered plot details for the episode, via casting calls put out for the episode’s guest stars.

Koracen, a Replicator scientist on Weir’s ship, believes he has found a way to reach a digital equivalent of ascension. Their consciousnesses will be enabled to exist indefinitely as fields of energy. As such beings they can essentially upload their minds to subspace and let their nanite bodies disintegrate, allowing them to move freely about the galaxy at will.

Lia, another Replicator, is understandably skeptical. But Koracen has a willing volunteer, and demonstrates the procedure.

Later, in Atlantis, the team works furiously to regain access to a room they have been locked out of. Colonel Sheppard orders two officers to retrieve heavy arms and explosives to blow the sealed door, but there is no need. The door suddenly opens, and Sheppard and his team are shocked by the familiar face which greets them.

Fran (Michelle Morgan) is reconstituted by the Replicators in Atlantis.

It is Fran (Michelle Morgan), the “Friendly Replicator ANdroid” engineered by Dr. McKay last year (“Be All My Sins Remember’d”). Apparently now missing their bodies, the Replicators have come to Atlantis. And their leader is someone very, very close to the Atlantis team: Elizabeth Weir herself.

Weir will not be played by actress Torri Higginson, who turned down the offer to appear in the episode (story). Instead the script was rewritten so that the cliffhanger could be resolved and the story continued without her.

The existence of disembodied Replicator consciousnesses in the episode may go a long way in explaining just how this science fiction feat will be accomplished — if the Weir from “Be All My Sins Remember’d” was, in fact, a Replicator duplicate and not the human Weir, who the Replicators claimed had been killed (“This Mortal Coil”).

“Ghost In the Machine” also guest stars David Nykl as Radek Zelenka. Written by Carl Binder and directed by Ken Girotti, the episode is expected to go before cameras in a few weeks.

Visit GateWorld’s Season Five episode guide for more on the upcoming season! New episodes return to SCI FI Channel in the U.S. in July.