Star Trek: Discovery kicks into the propulsive second chapter of its three-part season finale this week, “There Is A Tide…,” as the captured starship becomes the setting for the Emerald Chain’s endgame at Starfleet Headquarters.

I love a good episode in which our heroes must retake their ship — a longstanding Star Trek tradition, in classic episodes like “Basics,” “Chosen Realm,” “Shockwave,” and, um, “Rascals” — and now Discovery gets its time to play with the genre, even moreso than during Harry Mudd’s chaotic time loop escapade in Season 1.

With a tight script from Kenneth Lin — and the usual great pacing from six-time Discovery director Jonathan Frakes — this episode is fast, exciting, and action-packed, delivering some thoughtful and surprising world-building that expands our understanding of the politics of the 32nd century.

The episode opens with Discovery under Osyraa’s (Janet Kidder) control, and includes a return of Zareh (Jake Weber), the human antagonist last seen heading out into the parasitic ice in “Far From Home.” On the one hand, it is a delight to see Jake Weber return, because he is an extremely capable actor who gives Zareh an air of confident menace.

However, the decision to bring back Zareh — who we previously thought was just some pirate raider in a forgotten system — as a high ranking member of Osyraa’s team, makes the galaxy feel very small.

Given how hard it should be to travel across that galaxy with the absence of dilithium, it feels like a mistake to make it so easy for characters to show up wherever they please. Discovery can do it because it has a spore drive. But if the show’s conceit for this season is that the galaxy has become factionalized and hard to traverse, reintroducing Zareh undercuts that.

After hurriedly catching up to the captured starship by way of dangerous courier subspace corridors, Book (David Ajala) and Michael Burnham (Sonequa Martin-Green) implement their own take on Emergency Landing Plan B, crashing Book’s ship into Discovery’s open shuttlebay to get aboard before it manages to breach Starfleet Headquarters’ defenses.

From here, the show divides into several main plot lines that run throughout the episode.

The first involves Burnham, who works to evade Emerald Chain soldiers, or “regulators,” as she makes her way to engineering. She is injured in an early confrontation with a regulator, which makes her efforts much more difficult. Burnham’s injury certainly raises the dramatic stakes and requires her to rely more on her brains than brawn… but it stretches my suspension of disbelief somewhat that when phasers transform to fit on your wrist and transporters are housed within a combadge, there was not a medkit anywhere between Discovery’s shuttlebay and engineering? That seems like a serious health and safety lapse.

As she makes her way through the ship, we get to learn some more about the Emerald Chain as captured Paul Stamets (Anthony Rapp) is left to be interrogated for spore-drive secrets by Chain scientist Aurellio, played by returning guest actor and fan favorite Kenneth Mitchell.

Like Mitchell’s real-life requirement, the scientist is confined to a wheelchair due to a genetic defect; Osyraa saw Aurellio’s potential, and used Emerald Chain resources to make sure he had the right treatments, leading him to become one of the Chain’s most prominent scientists.

The actor, who publicly revealed he is suffering from ALS in February, turns in a quietly commanding performance as the Emerald Chain scientist who, while shielded from many of Osyraa’s crimes, has a deep well of loyalty for her. It’s a far cry from the scenery-chewing appearances by Mitchell in his Klingon roles in past seasons, but it’s an affecting performance that takes us deeper into life in the Chain.

(As the episode progresses and Aurellio begins to witness some of Osyraa’s more ruthless tactics, it is clear he is conflicted about them. I hope and expect we will see more of Mitchell in the season finale to continue playing out that conflict.)

The first two stories collide in perhaps the season’s most emotional moments, as Burnham rescues Stamets from his captivity, and — over his extremely vocal protests — successfully executes her plan to evacuate him (explosively) from Discovery and away from Osyraa’s clutches.

The only issue with that, though, is that Stamets — who is driven by concern for both Culber and Adira, each stuck back in the radiation-soaked Verubin Nebula — does not want to leave the ship.

It’s a heartbreaking moment for the two characters, weighing Burnham’s duty to Starfleet (which she seems to have realized in this instance takes priority) against Stamets’ love for Culber and Adira, and sense of betrayal that Burnham would pursue this action without his consent. Anthony Rapp has not had many big emotional beats this season, and as he rages against Burnham’s actions, he reminds us what a great actor he is.

Up on the command levels, Sylvia Tilly (Mary Wiseman), Ryn (Noah Averbach-Katz) and the ship’s bridge crew — Detmer (Emily Coutts), Owosekun (Oyin Oladejo), Bryce (Ronnie Rowe, Jr.), Rhys (Patrick Kwok-Choon), and Ina (Avaah Blackwell) — are under lock and key in Saru’s ready room.

The scenes between these characters are great, as the bridge crew work together to distract the guards and disarm them, and then follow Tilly as she immediately takes command of the next steps and begins developing a plan to retake Discovery… along with some assistance from an unexpected friend.

After a few brief assists earlier in the season, it seems that Zora (voiced by Annabelle Wallis) — the manifestation of the Sphere Data living inside Discovery’s computer systems — was able to hide herself in a set of DOT-23 repair drones when the Emerald Chain hijacked the ship’s operating system. I’m excited to see how that plays out in the season finale!

Perhaps the most interesting story of the week, however, is one separate from all the action and fight scenes: the negotiation between Admiral Vance (Oded Fehr) and Osyraa, in which she reveals that the Chain has hijacked Discovery not to destroy Starfleet, but to propose a peace agreement between the two organizations.

We learn that Osyraa is actually a ‘minister’ in the Emerald Chain, a politician who has bigger designs for the relationship between the Federation and the Chain than simply just perpetual conflict.

Osyraa proposes an alliance with the Federation: as part of the proposal, the Emerald Chain would agree to shut down its slave markets and its endorsement of the slave trade, remove its influence from pre-warp civilizations, and commit to peaceful relations with the Federation. In exchange, the Federation would be required to endorse the Chain’s mercantile economy and normalize relations… effectively merging the Federation and the Emerald Chain into a single body.

Vance is extremely tempted, and acknowledges that the proposed armistice presented by Osyraa shows they have made significant concessions — but he askes for the one thing the Orion simply can’t agree to: her own surrender.

It’s a fascinating moment for a Federation that has laid low and being offered an opportunity to rebuild itself. Vance clearly wants to find a way to take the deal, but he cannot compromise the Federation’s “moral clarity” any further, refusing to allow Osyraa the opportunity to serve in Chain leadership without bringing her to justice for her crimes.

And so the deal is off. Where it heads from here in the finale is unclear. Osyraa returns to Discovery intent on regaining control of the ship, but it was fascinating to see that the Emerald Chain seem to be a much more complicated faction than the show previously indicated… and that the Federation is more tired and threatened than it has ever been.

I hope these dynamics continue to be explored as the show heads into Season 4.

OTHER OBSERVATIONS

• In a fairly obvious series of homages to Die Hard, Burnham has to crawl through a Jeffries Tube, she loses her shoes, and then gets on the radio to taunt the lead bad guy before running off to save the day. (At least she didn’t have to walk across broken glass to do it.)
   
• The dangerous courier network — some kind of subspace corridor or transwarp conduit — are filled with debris and parts of wrecked starships, much like the Vaadwaur Underspace of the Delta Quadrant, seen in “Dragon’s Teeth.”
   
• Burnham uses her skills with the Vulcan neck pinch to knock out Stamets in the engineering bay, last seen in use on Captain Georgiou in “The Vulcan Hello.”

• The 32nd century Starfleet phasers fire blue energy beams; with a few occasional exceptions in the TOS and Original Series film era, the vast majority of all Starfleet hand phaser beams seen to date have been red-orange in color.
   
• Like hand phasers of years past, the new Starfleet phasers can also be set to overload; the normally-blue lights on the weapon’s upper section change from green to yellow to flashing red as the energy buildup reaches explosive levels.
   
• The new phaser design also features a green light on the front of the weapon, where the energy beam emanates.

• Stamets tells Aurellio that he’s got a child — referring to Adira — but while the two characters have certainly started to bond over the last few episodes, that kind of serious familial attachment seems like it’s coming out of nowhere. It’s one thing to take a young friend under one’s wing as a mentor figure, but quite another to claim the role of their father — though to be fair, it could simply be Stamets’ way of trying to throw Aurellio off his game.
   
• One of the destroyed ships in the courier tunnel is a Orion Wanderer-class vessel, a design created for the mid-1980’s FASA Star Trek role-playing game.
   
• The president of the 32nd century Federation is mentioned several times in this episode, but is neither referenced by name nor gender. Perhaps when we finally get to meet them, it’ll be a familiar face whom we know made it to the far future?

• The Emerald Chain regulator Burnham sends into space is played by Lisa Berry, better known to Supernatural fans as Billie the Grim Reaper. Her species is the same as young Kima from the Picard Short Trek “Children of Mars.”
   
• Osyraa knocks the replicated apple as not quite tasting right, a longstanding Trek trope about replicated food not measuring up to “real” food.
   
• Starfleet station Deep Space 253 is a far-flung Federation outpost that has been trading with the Emerald Chain for nearly a century, implying there may be other outposts and ships that continue to operate on their own — much like the liaison office Burnham visited in the season premiere.

• One of the Starfleet vessels parked at headquarters is the USS Song (NCC-325084).
   
• Zora’s trio of DOT-23 units have colored eyes which match the standard Starfleet assignment divisions: red, blue, and gold.
   
• The stardate on Osyraa’s armistice document reads “STARDATE 29141429.1,” which is well outside the (correct) range of 32nd stardates established in “People of Earth.”
   
• It seems likely that Burnham’s mayday message to her mother — who we know is still on Ni’Var — will result in the arrival of combined Vulcan/Romulan forces. If they come to save the day, it’ll be the fourth Trek season finale in a row to have our heroes rescued at the last moment by outside help, after the Klingons and Kelpiens in “Such Sweet Sorrow, Part 2,” Riker and the Starfleet armada in “Et in Arcdia Ego, Part 2,” and Riker and the Titan in “No Small Parts.”

Overall, though, “There Is A Tide…” doesn’t quite stand on its own particularly well. It’s full of action-packed and tragic moments alike — like Rhys and Bryce’s tactic to fool their Chain captor, and the execution of world-weary Ryn — but largely ignores everything “Su’Kal” set up about The Burn (likely to be a major part of next week’s finale).

There is a lot of story left for this show to resolve in the year’s one remaining episode, and hopefully the season’s last outing will not only stick the landing, but set up a solid jumping-off point for Season 4’s adventure.

Star Trek: Discovery concludes its third season with “That Hope is You, Part 2” on January 7 (on CBS All Access and CTV Sci-Fi Channel); international viewers get the finale on Netflix on January 8 in all other global regions.