Warning: SPOILERS for Star Trek: Discovery Season 3, Episode 11 - "Su'Kal"
With "Su'Kal," the 11th episode of season 3, Star Trek: Discovery finally joins in on a Star Trek tradition with its own holodeck episode - but with an unusual twist. "Su'Kal" finally solved the mystery of who and what caused The Burn, the dilithium catastrophe that completely changed the course of the galaxy in the 32nd century. It turns out the unwitting culprit was Su'Kal (Bill Irwin), a Kelpien living in an elaborate holodeck simulation aboard the KSF Khi'eth, a research vessel that crashed within the radioactive Verubin Nebula 125 years ago.
Holodecks and holodeck episodes have been a fan-favorite trope ever since they became a staple of Star Trek: The Next Generation, Star Trek: Deep Space Nine, and Star Trek: Voyager. Although Star Trek: The Animated Series introduced the holodeck in the 1970s, it was TNG that popularized the virtual reality environment with unforgettable episodes like "Elementary, My Dear Data," "Qpid," and "Ship in a Bottle." On DS9, the holosuites in Quark's Bar were the source of classic episodes like "Our Man Bashir," "It's Only a Paper Moon," and "Take Me Out to the Holosuite." Star Trek: Lower Decks just delivered an all-time great holodeck episode with "Crisis Point," which hilariously homaged the Star Trek movies. However, the holodeck became a canonical part of Starfleet ships in the 24th century; therefore as a 23rd-century starship, the USS Discovery had no holodeck before it permanently jumped into the 32nd century for Star Trek: Discovery season 3.
In "Su'Kal," an away team consisting of Captain Saru (Doug Jones), Commander Michael Burnham (Sonequa Martin-Green), and Dr. Hugh Culber (Wilson Cruz) beamed into the Khi'eth to find the Kelpien living alone, only to realize they'd transported into the elaborate holodeck program built by Su'Kal's late mother, Dr. Issa (Hannah Spear), to educate her child and keep him company. The Khi'eth's holodeck even transformed the Starfleet Officers, turning Burnham into a Trill, Culber into a Bajoran, and Saru into a human (which allowed Doug Jones to appear in the episode without his Kelpien prosthetics for the first time). Discovery's away team interacted with several Starfleet characters who were part of the program, but they were also plunged into a nightmare scenario that was like a Kelpien version of a horror movie because the holodeck has been malfunctioning for years due to the radiation within the Verubin Nebula.
One of the fascinating aspects of "Su'Kal" was seeing Burnham, Saru, and Culber cope with being inside a holodeck, which was a new experience for all of them. They were quick to realize they were in a holographic simulation, and Saru knew enough to call for the exit but to no avail, since no archway materialized due to the malfunctioning program. And because the Khi'eth's holodeck not only changed Saru, Michael, and Hugh's physical appearances but also took away their tricorder, weapons, and the vital meds they needed to survive exposure to the Verubin radiation, Discovery's crew had to adapt to the rules within the program and its nightmare scenario.
Although it hasn't been stated in an episode yet, ever since Saru's starship was retrofitted with 32nd-century technology, the recommissioned USS Discovery-A now has a holodeck of its own. This was confirmed in the canonical log entry by Commander Jett Reno (Tig Notaro) in the @startreklogs Instagram. A holodeck is just one of numerous new additions to the thousand-year-old starship like programmable matter, detached nacelles, and even a cloaking device. But with only two episodes left in season 3, fans will likely have to wait until Star Trek: Discovery season 4 for another holodeck episode where Discovery's crew will deal with the classic Star Trek trope of their own holodeck going on the fritz and endangering everyone aboard.
Star Trek: Discovery Season 3 streams Thursdays on CBS All-Access and Fridays internationally on Netflix.