By bringing in a rival with surface similarities, “Old Friends, New Planets” articulates the Ensign’s true self and how much she’s grown.

Nick Locarno (Robert Duncan McNeill) is the perfect antagonist for Beckett Mariner (Tawny Newsome) because he is her dark-tinged mirror image. Like Mariner, Locarno is a self-styled rebel who wants to hold onto his independence despite the rigidity of Starfleet. Like Mariner, he’s a brash whiz kid whose disdain for the rules gets him into trouble. And like Mariner, he comes with a certain lower decker pride and solidarity.

So when Nick aims to unite the underappreciated cast-offs from across the quadrant, to throw off the shackles of their know-nothing commanders and form an independent, unaligned “Nova Fleet,” it’s easy to see it as something a disgruntled Mariner might do herself if burned too badly by Starfleet’s strictures. In many ways, Locarno is a glimpse of the person Mariner herself could have become for want of a nail. Nick, and the show, want you to think that he and Beckett are two sides of the same coin, at least at first.

But the trick is that despite those surface-level similarities — the rebellious bent, the rule-breakers’ glee, the bristling at protocols and limitations — Mariner and Locarno couldn’t be more different.

Ultimately, what distinguishes them is simple and reveals itself in the opening flashback to their days at Starfleet Academy. While Cadet Wesley Crusher (Wil Wheaton) frets over Nick’s dangerous plan for graduation, a young Mariner gushes to Cadet Sito (Shannon Fill) about immersing herself in the Academy. But for his part, a dismissive Locarno focuses on nothing but pulling a stunt that will earn him a place in school history.

At heart, even all these years later, the two of them never really changed. Despite her protestations, deep down, Beckett Mariner still cares deeply about Starfleet. And despite his protestations, deep down, Nicholas Locarno only cares about himself.

Those differences aside, there’s a lot going on in “Old Friends, New Planets,” the finale to Lower Decks’ superb fourth season. Locarno reveals his scheme to assemble the unseen and unwanted of the galaxy into his own rebel contingent. Mariner nabs the dangerous Genesis Device he’s using as leverage against the interstellar governments who might intervene. The episode is, in many ways, the culmination of not just the mysterious destruction and abduction plot that’s been playing out since the first episode but scads of storylines big and small that have wound their way through this year of the Cerritos’ mission.

In a season that’s shown how bold and capable Captain Freeman (Dawnn Lewis) can be, she cuts through diplomatic gridlock, defies orders, and makes a daring effort to rescue a member of her crew and a member of her family, in the proud tradition of Captains Kirk and Picard. In a season that saw Rutherford (Eugene Cordero) rank up despite his rivalry with Ensign Livik, the two young officers settle their beef through the magic of impersonating Mark Twain, and work together long enough to devise a plan to break through Locarno’s shield.

Despite her protestations, deep down, Beckett Mariner still cares deeply about Starfleet. And despite his protestations, deep down, Nicholas Locarno only cares about himself.

In a season where Boimler (Jack Quaid) worried about, rather than salivated over, the prospect of inching closer to the captain’s chair, his steady growth this season pays off in a rousing moment when he becomes Acting Captain of the Cerritos (and even gets to tell off an admiral in the process). In a season where T’Lyn (Gabrielle Ruiz) struggles over where she fits in, the off-beat Vulcan affirms the peculiar logic of being “Cerritos Strong” and chooses to stay aboard the ship with her new Starfleet colleagues and friends, despite an opportunity to return to her old vessel. 

And most of all, in a season where Tendi (Noël Wells) begins to resolve her complicated relationship with her Orion heritage, she turns to her home planet and her sister for help in her crew’s rogue mission, even resorting to “barter by combat” to get it. Her willingness to give up her commission in Starfleet in exchange for D’Erika’s assistance adds a bittersweet note to the finale’s triumphs and opens the door to storylines for season 5.

Even for an extended episode like this one, though, these moments and character beats could do with a little more real estate to land with full impact. But as much oxygen as the Mariner-Locarno confrontation rightfully consumes, it’s nice that Lower Decks takes time to honor the journeys each of its major characters has taken this season as well.

Likewise, despite the blockbuster happenings, the show still finds time for some winning humor and great visuals. Writer May Darmon crafts plenty of great comedy for the episode, with smaller gags like Chief Engineer Billups becoming incensed when D’Erika besmirches the honor of the Cerritos, running jokes like Mariner chatting with the Genesis Device as though it’s her first officer, and plot-relevant laughs when Locarno can’t disarm a Ferengi bomb because it’s behind a paywall. Moments like these all add a nice bit of levity to one of the show’s more dramatic installments.

Plus, director Bob Suarez and a stellar team of animators make this one feel special: from smaller animation touches like Dr. Migleemo “fluffing his down” or Mariner’s expressions when telling the galaxy that Nick is out of his mind to big-time moments like Beckett zipping through a convenient pocket of space debris or the Cerritos effectively shot putting an Orion worship through a Trynar Shield. The dynamism of the animation, the beauty of the imagery, and the kineticness of the pursuit all make “Old Friends, New Planets” stand out for its craft alone.

And yet, at the end of the day, the finale comes down to that juxtaposition of Beckett Mariner and Nick Locarno. Because yes, Mariner saves the day with bold moves and daring choices. She steals a Genesis Device out from under the bad guy’s nose, dodges enemy fire in unfamiliar territory, and sets the bomb off in open space at grave risk to herself so it can’t be used as a weapon of war.

But she honors Starfleet principles through it all. Mariner never shoots to kill. In fact, the way she ultimately undermines Locarno has less to do with bombs and phasers and more to do with exposing his selfishness to his allies. In the end, Mariner wins by sowing dissent among “Nova Fleet.” Her approach is the kind of diplomatic, interpersonal resolution that Captain Picard (not to mention her mom) would be proud of.

In the final tally, Nick Locarno isn’t Starfleet. And more to the point, no matter where he ranked in his class, with values like that, he never was.

By contrast, in Locarno’s actions rests an inherent critique of the people who take on the mantle of rebels and reformers, shouting to the high heavens that this system or that one is irrevocably broken, but whose solutions reveal that, ultimately, they’re only in it for themselves.

Nick claims to be founding a “coalition of equals” but still demands to be in charge. At the end of the day, whatever blather he spews, whatever superficially appealing rationales he offers for his actions, all Nick wants is power and the chance to feed his ego. He doesn’t believe that Starfleet’s lost its values; he’s just miffed after being thrown out of the Academy for endangering his fellow cadets. And in the same vein, he shows he still doesn’t care about safety, valuing destruction over defense. In the final tally, Nick Locarno isn’t Starfleet. And more to the point, no matter where he ranked in his class, with values like that, he never was.

Mariner is, though. What separates her from Locarno is that even as one of Starfleet’s most vocal (and amusingly obnoxious) critics, she believes in its mission and principles. She bends the rules but knows why they’re there. She’d rather try to talk her way out of trouble than blast her way out of it. And despite everything, despite the self-destruction Nick sowed for himself with this whole scheme, she still tries to save him with the nobility and compassion that are the trademarks of Starfleet’s best. 

It’s part and parcel with the poetry of the episode’s ending. In that opening flashback, Sito pushes back on Nick’s claim that trying this dangerous maneuver at graduation will mean everyone remembers them. She scoffs, “I bet the only name anyone’s going to remember is Locarno.” And whether she believed it or not, she was right. When the Genesis Device explosion consumes Nick, Starfleet decides to name the resulting planet after him since his atoms were contained in the interstellar soup, with an aim toward making it a home for refugees.

It’s not the legacy Nick intended, but it is, oddly enough, the one he earned. The irony is that Nick was all about ego despite claiming he wanted to create a place for all the cast-offs across the galaxy. And while not in any way this selfish man ever intended, Nicholas Locarno ended up doing just that.

Mariner’s legacy is not yet written. She still has time to rise to her potential and take her place among the greats, especially now that she’s worked through some of her deepest psychological scars. But for all her miniature rebellions, for all her resistance to ranking up, for all her playful mischief aboard the Cerritos, what separates her from the Nick Locarnos of the world has always been clear — whether she admits it or not, Beckett Mariner is, and always has been, pure Starfleet.