Star Trek: Deep Space Nine
S2 E16 Shadowplay On a planet in the Gamma Quadrant, Odo and Dax discover a society whose inhabitants are mysteriously disappearing into thin air.
Stargate SG-1
S4 E13 The Curse Daniel Jackson returns to college when one of his former professors, Dr Jordan, dies unexpectedly in a lab explosion. Unconvinced that his death was accidental, Daniel discovers that Dr Jordan was studying an ancient Egyptian Goa'uld symbiote, which he fears may now be running loose on campus.
Star Trek: Voyager
S7 E24 Endgame A time traveller forces Captain Janeway into a deadly showdown with her nemesis, the Borg Queen, and a romance ignites during Voyager's peril.