WARNING: The following article contains spoilers for this week's episode of Star Trek: Discovery, "The War Without, the War Within," which premiered Sunday on CBS All Access.
Viewers knew from the very beginning that, because of its place within the franchise timeline, Star Trek: Discovery would have to provide an explanation for why the vessel's experimental spore drive -- the Federation's last best hope in the war with the Klingons -- didn't become standard issue within Starfleet. Sure, the wondrous device comes with risks (just ask the tardigrade, Lt. Stamets, and the crew of the U.S.S. Glenn), but surely all of those kinks would be worked out by the time of Enterprise's five-year mission a decade later. Probably, if only the drive didn't bring with it the possibility of not only leaping across the known universe, but into an alternate one.
In last week's episode, the Discovery crew, minus Captain Lorca and poor Dr. Culber, fought their way out the Mirror Universe, only to realize they'd arrived home nine months into the future, where the Klingon houses are on the cusp of victory. With Starfleet and the Federation virtually decimated, Admiral Katrina Cornwell (Jayne Brook) has no patience for talking: In this week's episode, "The War Without, the War Within," she leads an armed boarding party, which includes Sarek (James Frain), seizes control of Discovery, and demands answers -- about Lorca, and about where the hell the Federation's secret weapon has been all this time.
She gets more than she expected, however, with a story about alternate realities, two versions of Discovery, and Lorca's byzantine scheme to return to his own universe and overthrow its Terran emperor (who, by the way, is now in this universe). But in the process, Cornwell lays the groundwork for how the series intends to handle those story elements that could pose a problem for the continuity of Star Trek: The Original Series, and everything that follows. In the debriefing, she updates Discovery's officers on the state of the war, which has turned decidedly in the Klingons' favor as the 24 individual houses essentially compete for victories against the Federation, with some resorting increasingly to large-scale suicide attacks. Discovery will reenter the battle, she orders, but only after all evidence of its jump to the Mirror Universe is classified and destroyed.
"We cannot risk the knowledge of this alternate universe leaving the confines of Discovery," Cornwell declares, not yet aware that the ship brought back an honored "guest" in the form of Emperor Georgiou.
"It would be ... too many possibilities," Stamets explains to a disbelieving Michael Burnham. "Indeed," Sarek concurs. "Our people have suffered terrible losses. What would you do if your dead wife, your lost child, your murdered parents might be alive on the other side, and that technology exists for you to see them again? This knowledge must be buried."