Surrounded by the wreckage of what appear to be multiple, unknown Klingon vessels, the crew of the Discovery attempt to determine where they have arrived after their final, ill-fated spore-drive jump. Captain Lorca and the crew have little time to process their surroundings before an approaching Vulcan vessel opens fire on Discovery, much to everyone’s surprise. Fortunately the Vulcan threat is neutralized by the U.S.S. Cooper, however the Discovery crew is still puzzled by the series of events. Lorca, however, has a theory.

Off the bridge, the captain explains to Burnham and Saru that he and Stamets had suspected the mycelial network could lead to parallel universes. The 133 spore drive jumps Discovery has taken, he theorizes, made travel to such an alternate reality possible. To begin to grasp their surroundings, Captain Lorca sends Lt. Ash Tyler on an exploratory mission to retrieve a data core from the Klingon wreckage. Meanwhile in sickbay, Stamets’ condition is dire as the Engineer remains unresponsive and, alternatively, incohesive. Given his condition, it becomes clear to Lorca that the Discovery’s return to their own universe will not occur via the spore-drive system that brought them here.



After Tyler returns from his mission to retrieve the Klingon data-core from the wreckage, he visits the still-imprisoned Klingon L’Rell to inquire about his increasing bouts of PTSD. The Klingon convinces Tyler to release her; when he does, she begins to speak in her native tongue and triggers Tyler to respond to her in Klingon. After he snaps out of it, a confused Tyler locks L’Rell back into her cell and flees the brig.



Burnham analyzes the data and learns about the Terran Empire; an oppressive, racist, xenophobic culture that rules all known space, and is led by a faceless Emperor. The existence of the human-only organization explains certain inconsistencies — like why Vulcan and Andorian bodies littered the Klingon wreckage. In this universe, alien species have allied to fight back at the oppressive human regime.



When the U.S.S. Cooper reappears and opens a communication line with Discovery, Burnham prevents Lorca from speaking because in the Terran Empire, he isn’t the ship’s captain. Cadet Sylvia Tilly occupies that role, and is forced to masquerade as the ship’s commanding officer. In order to pass as Terrans while they figure out a way home, the crew begins the process of rebranding themselves and their ship, now dubbed the I.S.S. Discovery. The crew don new Terran uniforms, ship displays are adjusted, and they begin to learn about – and adopt - their counterpart’s personas.



Using the rebel intelligence taken from the data core, Burnham explains to Tilly that to Terrans she’s a ruthless captain known by monikers like “the Slayer of Sorna Prime,” “the Witch of Wurna Minor,” and “Captain Killy.” As for Lorca and Burnham, they were considered crucial players in the Terran Empire, until Lorca initiated a rebellion against the despotic emperor, killed the Terran Burnham, Captain of the I.S.S. Shenzhou, when she attempted to intervene, and struck out on his own.



Tyler, still troubled by his encounter with L’Rell, visits with Dr. Culber in sickbay where he asks the doctor if he can identify any odd experiments the Klingons may have performed while he was in captivity. After analyzing deep scans of the Lieutenant, Culber tells the security officer that the Klingons performed “bone-crushing” procedures on him that have transformed him both mentally and physically. It seems, in fact, that the Klingon Voq and Lt. Tyler are one in the same. When Culber attempts to prevent Tyler from joining an away missing, given his new found identity, Tyler/Voq quickly snaps his neck, killing the doctor instantly.



Tyler arrives at the transporter chamber, where he meets Lorca and Burnham. The trio prepare to transport to the I.S.S. Shenzhou after concocting an elaborate plan. As Lorca and Burnham explain to Saru, they’ve discovered that another Starfleet vessel, the U.S.S. Defiant, previously stumbled into the Terran universe. By accessing Terran databases, they can ascertain how the Defiant returned to its proper timeline. To do so, Burnham returns to the Shenzhou with the “captured” traitor Lorca. “Captain” Tilly initiates contact with the ship and its new captain, Danby Connor, to set the plan in motion.



Once she transports aboard the Shenzhou with Lorca and Tyler, Burnham asserts her dominance over Connor, per Terran custom, refusing to let the officer or his crew take possession of Lorca lest they take credit for the fugitive’s capture to curry the emperor’s favor. She intends the move to protect Lorca from excessive Terran torture, though even she can’t figure out a believable reason to spare her companion from agonizer booth. When Burnham finds herself alone in a turbo-lift with Connor, he attempts to murder her to solidify his command and the fealty of his underlings. Burnham kills him in defense, and when the turbo-lift door opens to the bridge, Connor’s dead body falls to the floor as Shenzhou’s officers begin to chant, “Long live Captain Burnham! Long live the Empire!”