Kira and Bashir are flung into a mirror universe.
An accident in the wormhole sends Kira and Bashir into the mirror universe, where, after Kirk's visit a century earlier, an alliance of Klingons, Cardassians and Bajorans has enslaved the Terrans. The station is a mining station run by the Intendant, Kira's double, with Garak as her second and Odo overseeing slave labour.
The Intendant takes an interest in Kira, while Garak plots to use her to replace the Intendant. Bashir escapes from the ore processing area, killing the mirror Odo in the process, and convinces the beaten-down O'Brien to help. When they are about to be executed, O'Brien's speech moves the mirror Sisko, who helps Kira and Bashir return home.