Stranded in the mirror universe, Discovery poses as its Terran counterpart, and Tyler's hidden conditioning drives him to kill Dr. Culber.
Discovery finds itself in a universe ruled by the brutal Terran Empire. To blend in, the crew disguises the ship as its Terran counterpart, with Tilly playing the role of its ruthless captain, while Stamets lies unconscious. Burnham learns that her own mirror self, captain of the ISS Shenzhou, is presumed dead.
When Dr. Hugh Culber tells Tyler that his body shows signs of extensive surgery, Tyler's hidden conditioning takes over and he kills Culber. Burnham then poses as her counterpart and goes to the ISS Shenzhou with Lorca as her supposed prisoner, and Lorca is thrown into an agony booth. Jonathan Frakes directed from a script by Sean Cochran.