A triumphant mystery box to unravel and behold, “Su’Kal” is an imaginative, clever hour of science fiction that harkens back to a number of classic storytelling tricks from Star Trek’s past — and starts an unofficial three-part season finale that will likely answer many of the central mysteries of Star Trek: Discovery’s third season.

The strength of this story comes in the activity on a planet of dilithium found deep inside the Verubin Nebula, where Discovery has detected a survivor on board the Kelpien ship that sent out a distress signal coinciding with the origin of The Burn more than 100 years ago.

Captain Saru (Doug Jones) has surmised it is possible for someone to still be alive on that ship, since he believes the ship’s captain was pregnant in her original distress call. The crew jumps into rescue mission mode to locate the survivor, but immediately find themselves in peril trying to navigate the dense radiation inside the nebula.

Despite the dangers, Saru is single-mindedly focused on finding a way through to the planet, which Book (David Ajala) provides by taking his ship in for a closer, albeit still dangerous, look. His brief sojourn deep into the nebula uncovers a few revelations: a pocket above the planet for Discovery to jump safely in-and-out of to get an away team down to the stranded ship, and exactly how deep Michael Burnham’s (Sonequa Martin-Green) feelings for the Kwejian courier truly run.

While Book is in the nebula and getting beat up by the radiation, the look of distress on Burnham’s face is a revelation to herself and the audience as to the depths of how much she cares for him. For better or worse, the reveal feels important in terms of how Burnham’s arc will play out as the season approaches it conclusion.

With a plan in place to get to the survivor on the ship, Saru puts Ensign Tilly (Mary Wiseman) in charge of Discovery so that he can lead the away team. A sensible decision given the circumstances and one that amps up the narrative of this strong episode — but before getting to the away mission, the episode intelligently slows down to share three quiet scenes to help build the stakes for what is to come.

First Burnham tells Book she’s concerned that Saru won’t be able to objectively make the big decision required of the captain’s chair, something we’ve seen percolating throughout the season. Then Dr. Culber (Wilson Cruz) calmly explains to Paul Stamets (Anthony Rapp)  that despite his nervous partner’s protestation, the doctor is motivated by his newfound purpose in the 32^nd century to help someone that might have been living alone for decades.

And finally, Burnham shares some encouraging words for Tilly about a metal burr under the arm of the captain’s chair that the Shenzhou’s Captain Georgiou rubbed away with her thumb, to help her stay calm and focused. There’s one on the Discovery’s captain’s chair, too, and she’s seen Saru do the same thing. “Burr, dent, shiny spot, whatever. It’s there for you. You belong in that chair, Tilly,” she tells her.

With Tilly in charge of the ship, the away team of Saru, Burnham and Culber beam down to the surface, where an absolute classic, humdinger of a Star Trek episode breaks out!

As seen previously in fun, augmented reality and holodeck episodes like “Spectre of the Gun,” “The Killing Game,” “Our Man Bashir,” “Qpid,” and others, when the away team materialize, their appearance and clothes have changed, and they seem to be inside some kind of a simulated environment on the Kelpien ship.

Burnham is now a Trill, replete with a beautiful red hood; Culber is a Bajoran, right down to his upgraded 31^st century silver ear-ring bling); and Saru is… human! The presentation of the famed prosthetic actor Doug Jones as a human is an absolute blast. Every moment for the beloved performer to appear on screen in his actual face is a joy, and Jones kills it.

Saru is Doug Jones, and for the first time we get to see how true that statement is without the extra accouterments.

It quickly becomes clear the trio are in a highly advanced, but degrading, holographic environment, designed to nurture and teach the Kelpien child left alone on the ship to survive. When the crew meets the holo-environment’s lone resident, they find a fragile, childlike Kelpien named Su’Kal — played with a youthful vigor by veteran genre actor Bill Irwin, most recently seen in FX’s Legion — who can’t comprehend anyone appearing from “outside.”

He runs away from a large, locked door that contains a monster embodying his darkest fears, which we later learn he must face in order to leave the environment and be truly free.

But before we get to that “burning” story point, the Discovery trio splits up, which leads to a fabulous scene between Su’Kal and Burnham. The moment between the two actors features Sonequa Martin-Green at her glorious best, with her amazing range on full display. Additionally, the writing is smart and crisp and works in partnership with the themes of the entire third season of Discovery.

To gain his trust, Burnham poses as a part of the training program, explaining to him “that for sentient beings, connection to others is incredibly important. It helps sustain them.” Su’Kal says he had not expected to find something new, believing the “outside” is probably dead by now.

He eventually gets spooked by Burnham as she pries deeper into his family and the time “before all of this.” He asks her to reset her “program,” which she does, but when she tries to query him again, this time about the “exit,” it’s all too much for his simple perceptions and he runs away for a second time.

With the trio reunited moments later inside Su’Kal’s protective fortress, they see the Kelpien building a totem to ward away his fears, but they don’t help: as the creature in the program lashes out at him, his fearful reaction causes an intense atmospheric disruption that reaches all the way outside the Nebula to Discovery.

Although the away team doesn’t realize it yet, Su’Kal’s outburst has knocked systems offline on Discovery and has threatened to destabilize the dilithium in the ship’s warp core. Culber has said a couple of times that for Su’Kal to have survived this long on a dilithium planet with massive subspace radiation, he has likely undergone some kind of “triggering” mutation in utero… and now we know that trigger in Su’Kal is what caused The Burn.

During all that activity on the planet, Tilly has been guiding Discovery’s efforts outside the nebula, hoping to affect repairs on the ship to allow them to jump back into the nebula and beam the away team out before the radiation deadline hits.

Unfortunately, the bridge crew has detected a ship coming in hot and Tilly effectively deduces that it is Emerald Chain leader Osyraa (Janet Kidder), the season’s big bad who was less than impressive when she first appeared a few episodes prior in “The Sanctuary.”

Here, though, Osyraa begins to break through as a strong villain, who sneers dismissively at the sight of Tilly in command; the ‘acting captain’ however manages to put the tyrant in her place with a withering takedown courtesy Sigmund Freud. “You’ve just proven the idea of projection,” she tells Osyraa. “You tell me I’m a fraud, because deep down you feel like a fraud. Interesting. It’s not just a human defense mechanism. It’s galactic!”

From there, though, things start to go south: despite the protection of Discovery’s new cloaking device (!!!), the Orion boss gets the jump on the crew by beaming on board, securing Stamets with a fancy thought-control headband, and getting comfortable in the captain’s chair. While her first appearance in “The Sanctuary” was less-than-impressive, Osyrra’s second round with Discovery has definitely made the character a more substantial threat.

Book makes another run into the nebula to rescue the away team — with a stowaway Adira (Blu del Barrio) on board — but only retrieves Burnham, as Culber and Saru stay behind to find and extract Su’Kal from his make-believe world before he blasts another Burn out into the galaxy.

While Tilly is assured in her decision-making — and prepared to make the tough calls, which she does in ordering the ship to retreat while leaving the away team stranded on their radiation-soaked mission — Osyrra gets the final victory as she lashes her ship onto Discovery, using a mind-controlled Stamets to jump both vessels away from the nebula… straight for Starfleet Command.

OTHER OBSERVATIONS

• What kind of Star Trek alien will Adira transform into when they arrive to the holographic environment? Perhaps something subtle, like a Vulcan, or a more substantial transformation, like an Andorian or Tellarite?
   
• After a few weeks in hiding, Gray Tal (Ian Alexander) returns, sad that he can’t experience the physical world like Adira can, which seems to hint that his limited existence may soon be somehow expanded to the ‘real world.’
   
• It seems that Sara Mitich (Lt. Nilsson) must have been unavailable to film this week’s episode; while she gets mentioned in dialogue early in the episode, her bridge station is manned by regular Discovery background actor Avaah Blackwell (Lt. Ina), who usually portrays the big-headed alien Osnullus.

• Discovery now has a working cloaking device (that comes with fancy ‘Green Alert’ monitor graphics). After the survivors of the Romulan supernova joined with Vulcan, the Treaty of Algeron — which prohibited the Federation from using cloaking technology — would no longer seem to be necessary. (Captain Riker mentions that it’s still in effect as of 2399 in the Star Trek: Picard Season 1 finale.)
   
• As we learned in “Genesis,” sickbay doubles as a veterinarian’s office for cat owners.
   
• Su’Kal’s protective totems come from the Kelpien/Ba’ul history book, which illustrates that the terrifying Ba’ul pylon — called the “Watchful Eye” or “All-Seeing Eye,” which once culled innocent Kelpiens on Kaminar — eventually became into a symbol of protection after 900+ years of post-vahar’ai freedom.

• The dilithium planet is categorized as a Class-Y — or Demon-class — planet.
   
• The holographic Admirals who welcomed Kaminar to the Federation — an event that occurred in history some years prior to the 3060s — wear the same Starfleet combadge design as the late Senna Tal. Since Admiral Vance knew that Tal host, the current 3189-era badges would seem to be a relatively new design for Starfleet.
   
• The replicator-repair hologram first encountered by the away team seems to be full of glitches, as her uniform is a mash-up of Starfleet designs: a Next Generation-era combadge and rank pips; Discovery-era shoulder stripes, and upper-arm mission patches reminiscent of the Enterprise-era jumpsuit uniforms.

• Saru’s family keeps coming back! Hannah Spear (who played Saru’s sister Siranna in Season 2) played the deceased Dr. Issa in “Terra Firma,” and this week, actor Robert Verlaque — who played his father in “The Brightest Star” — portrays the holographic Kelpien elder.
   
• Osyrra’s takeover of Discovery is reminiscent of the “Basics” cliffhanger that ended Voyager Season 2; hopefully there are no alien cavemen or people-eating lizards in the near future!
   
• Including all nine television shows, Short Treks, and thirteen movies, next week’s “There Is A Tide…” will be Star Trek’s 800th produced tale.
   
• The stair-filled holographic environment was filmed on location at the disused Kingston Penitentiary in Ontario.

“Su’Kal” is a superb episode that expertly uses the metaphorical platform that has propped up Trek’s narrative form to tell a story about the connection everyone needs to sustain them.

For a story produced before COVID-19 changed the world, it contains a message that could not be more appropriate for a world in the midst of a global pandemic — a world looking for ways to unite and persevere.

Star Trek: Discovery returns Thursday, December 31 with “There Is A Tide…” on CBS All Access and CTV Sci-Fi Channel. International viewers get the episode January 1 on Netflix, in all other global regions.