Read also: the best live TV streaming services with free trial>

“Caves” is the gem of an already excellent season.

All of fiction, not just Star Trek, loves the trope of enemies becoming friends after being stuck together for whatever reason, and it’s not hard to see why. There is something simple but effective about people walking into a situation at odds with one another because of personal or political disagreements, finding themselves forced to work together given the usual peril, and learning more about themselves and each other in the process so that they walk away with a new understanding and appreciation for one another. Like a lot of venerable tropes in fiction, this idea returns over and over, not because writers are lazy but because, by gum, it works.

Then, you have to add in the budget-conscious Star Trek series of the 1990s. The Next Generation production team went to great lengths to construct a standing cave set for an early episode, which made it cheap for Star Trek to use again and again, all the way through Enterprise.

And why not? No troublesome location shooting. No complaints that all alien planets look like the Paramount backlot. Just nice, plausibly similar rock formations, over and over. It’s easy, then, to understand how various Starfleet pairs would end up trapped there again and again, from Geordi and a Romulan, to Odo and Kira, to Tom and B’Elanna.

The latest episode of Lower Decks, straightforwardly titled “Caves”, is both a spoof of, and a tribute to, these venerable ideas. It’s fantastic how genre-savvy Mariner ((Tawny Newsome) is here, griping about how these missions always end up in suspiciously similar caves like this one and recognizing the tropes at play with her usual dose of sarcastic wit. There’s a laugh of recognition to hear Beckett offer the same complaints stalwart fans have offered for years to the franchise’s reuse of familiar sets.

At the same time, “Caves” is a diverting format-bender, allowing each member of the original Lower Decks quartet to tell a story about their own “trapped in a cave” experiences. The approach is a nice way to comment wryly on the ubiquity of these types of plots in Star Trek while also using them for the same legitimate purposes the more serious shows do.

The result is a bunch of winning mini-adventures that see Boimler (Jack Quaid), Rutherford (Eugene Cordero), and Mariner each overcome some cave-related challenge du jour while growing closer with someone they’re otherwise at odds with. The episode is smartly constructed, with each flashback contributing some necessary knowledge that helps our heroes escape their cave predicament in the present while also contributing to the broader theme of the episode via these flashbacks.

“Caves” is a diverting format-bender, allowing each member of the original Lower Decks quartet to tell a story about their own “trapped in a cave” experiences.

The most purely comedic is Boimler’s, which sees him stuck with math prodigy/conspiracy theorist Steve Levi. Steve’s conspiracy nut persona is an amusing takedown of the “I do my own research” types, with some funny commentary from the show on the mix of fact and fiction that draws folks like Steve to this flavor of baloney.

The mini-adventure puts Boimler in the same comical conspiracy-debunking mode he was in when manning the Starfleet recruitment booth in “Reflections.” And there’s even a fun twist during the proceedings.

Boimler does eventually befriend Steve after learning “not to yell at [him] or something,” much to the chagrin of Mariner and company. But the real “enemies to friends” turn in the narrative ends up being between Levi and the Vendorians, who were at the center of his nonsense conspiracy. (The Vendorians are another trademark Lower Decks deep cut, a species that only appeared in The Animated Series.) A conspiracy nut learning his boogeymen aren’t so bad is a fun way to use the standard cave tropes for a solid laugh.

The most wholesome of the flashbacks (by Star Trek standards, at least) sees Rutherford and Dr. T’Ana stuck in a cavernous maze. Samanthan ends up giving birth to the clone baby of their dead alien guides (it’s a long story) while they evade a standard-issue cave monster that snarls and threatens their well-being.

This story is fun on its own terms. Here, it’s mostly Dr. T’Ana who does the warming up to things she normally dislikes, both babies and engineers, thanks to the magic of the cave. But the foes-to-friends transition also happens with the cave monster itself, who turns out to be a fellow parent simply trying to protect its own kids, in a characteristically Star Trek twist. Finding unique spins on the usual formula with these cave stories helps keep the episode lively and fresh, and grumpy T’Ana growing attached to both Rutherford and the unexpected tyke is downright sweet.

The most traditional of the three flashback plots sees Mariner leading the dreaded Delta Shift on a typical away mission gone awry. Their shuttle crashes into a cave (naturally), and the resource they need to escape is trapped within a strange energy field that makes you older the deeper into it you go.

This third tale is a hoot. The barbs lobbed between Mariner and her Delta shift counterpart, Ensign Karavitus (Artemis Dubois), have the right mix of snarl and snark. The black comedy of wunderkind Asif’s broken leg getting more and more messed up by the field until it straight up falls off is transgressive and oddly hilarious. And the reveal that there’s another cache of the material needed to escape sitting right above them in a much more pleasant youth field adds the right comic capper to the whole escapade.

But the wrinkle that puts this one in line with the other cave-bonding experiences is that it helps Mariner understand the plight of Delta shift and even begin to identify with them. The realization that they feel like they do the same job the day shift does but never get the senior staff facetime or recognition that Beta Shift does given their nighttime work is understandable and sympathetic. Mariner recognizes how that must feel and ends up on their side by the end, in a nice sign of her steady growth through the season and the series.

The growing emotional distance between them is sad, but there’s a well-observed note of truth to all of this.

And yet, to some extent, season 4 has involved our four core lower deckers growing apart. The overarching theme of the frame story is that since they’ve ranked up, Mariner, Boimler, Rutherford, and Tendi (Noël Wells) have all had more individual adventures. They aren’t as much a fixture in one another’s lives as when they started. Boimler didn’t spill about his acquaintance with Steve Levi; Rutherford didn’t tell his pals about birthing a kid, and Mariner definitely didn’t let it slip that she was friends with Delta Shift now.

The growing emotional distance between them is sad, but there’s a well-observed note of truth to all of this. It’s a reflection of how real-life close friends can drift apart, not because of disagreements or hurt feelings, but because life takes you to different places sometimes, and people naturally find themselves pulled in other directions. Friendships are like seasons, and that can be both sweet and sad.

But with that backdrop, it’s time for Tendi to tell her own trapped-together story (albeit one set in a turbolift, not a cave). Her tale ends up revealing the story of how our favorite quartet of ensigns ended up forging such a close bond in the first place. It’s a bit of a retcon to the series’ first episode, but suggests Mariner and company cemented their close bond thanks to being trapped together for hours and forced to get to know each other. Most importantly, it gave Tendi a heartwarming reassurance on her first day that, despite her insecurities as an Orion in Starfleet, she’d be able to find friends.

The episode ends on a sweetly comic note. The seemingly malevolent moss advances upon our heroes, only to reveal itself as sentient. After hearing all those soft-hearted cave stories, it wants to be their friends in an amusingly recursive twist. And the fact that the whole thing was, once again, orchestrated by the morality play-loving Vendorians is a riotous button to put on the whole thing.

But the bigger point of it all, and one that makes “Caves” the gem of the season to date, is that even if our favorite foursome’s lives move in different directions, they’ll always be friends. Cave or no cave, the four of them have been through a lot together. In miniature tales of cavern-stuck connections and in broader stories across fiction of people coming together through trials and triumphs, that experience means something. No wonder writers keep returning to the idea.

Apart from the crags and crevices, though, “Caves” is an affirmation of the notion that what happens when you’ve gone through something so intense together — whether trapped in a cave or a Cerritos turbolift — nothing, not even time and distance, or growing up and growing apart, can ever truly break your bond.