Sisko is kidnapped by O'Brien's counterpart from the mirror universe, and is cornered into assuming the role of his violent alter-ego and contact scientist Jennifer Sisko — the mirror version of his late wife — before she can develop a new sensor array that will mean the end of the rebellion.

Felecia M. Bell (Jennifer Sisko)
Max Grodénchik (Rom)
Tim Russ (Tuvok)
John Patrick Hayden (the Cardassian Overseer)
Dennis Madalone (a Marauder)

• The Terok Nor alternate universe was previously seen in the episode "Crossover".
  
• The command access code for Terok Nor is Alpha-9-1-7-5-Blue.
  
• Tim Russ' character from Voyager, Tuvok, makes an appearance in the mirror universe.