In the 13th Doctor's first season finale, Doctor Who cannot escape the pull of season-long arcs.
Ryan: Whatever happened to doors? Don't aliens bother with doors?
I often say that to watch 55 years (and counting) of Doctor Who is to witness the history of television. The early First Doctor episodes feel like watching stage plays with endless plywood sets. Throughout the next 20 years, the show goes color and then adds special effects as technology allows. The episodes go from eight or so stories per season, each comprised of four to six 25-minute chapters, to four stories, each involving two to four 45-minute installments, to the 13 episode traditional seasons fans know today.
The storytelling method also changes. Back in the 1960s, the idea of a "season-long story arc" was unheard of. When the show tried them under the Fourth and Seventh Doctor, it was a radical experiment. When the series returned in 2005, TV was only just undergoing a transition of focusing on "monster-of-the-week" tales to season-long mysteries. One can see Doctor Who's writers awkwardly experimenting with it in the first reboot season's "Bad Wolf" references. Since then, every season has had some sort of overarching theme tying the adventures together, from mysteries such as "The Face Of Boe" to the nature of Amy Pond and River Song's relationship.
When Chris Chibnall came aboard as showrunner this season, he insisted he would be pulling Doctor Who back towards the "Monster of the Week"-style show it used to be. This was a natural reaction to the Steven Moffat years, which focused heavily on season-long arcs. But in the end, the series cannot ignore modern audience expectations and the assumption a season finale will not only give closure to characters but tie in everything they have been through over the last 10-13 weeks.
The Season 11 finale opens with a series of nine distress calls all coming from a single planet named “Ranskoor Av Kolos,” which translates to “Disintegrator of the Soul." Nice vacation spot, that. The atmosphere apparently causes hallucinations and emotional distress, hence the name, so our companions are outfitted with blockers to keep them sane. It's a nice touch, keeping fans wondering when things from the past ten episodes turn up if they're real, but they are.
The Doctor: I think it's a precaution. I like precautions. Always take precautions. Especially when you don't know what you're doing.
Speaking of what's happening on the planet, all the leftover guest stars for this season are on it, starting with Paltraki (Mark Addy). He is hallucinating when they find him, but a blocker quickly fixes this, so the episode can get on with it. A message from Andinio (Phyllis Logan) suggests she might be manipulating things, but then Tim Shaw (Samuel Oatley) -- or Tzim-Sha, as the series revealed it is spelled -- breaks into the communication line. Remember him from the first episode, "The Woman Who Fell To Earth"? He and the Stenza, his race of murderous thugs, have been referenced a few times since then, mostly in the second episode, "The Ghost Monument." Sha starts killing people right away, taking out Paltraki's partner Umsang (Jan Le).
Seeing Shaw again gives Graham a new sense of purpose. Instead of whining and complaining, he's now 110% in with retracing Paktraki's half-remembered steps to locate remaining kidnapped crew. Graham's on a revenge mission, much to the Doctor's horror. She tells him if he goes through with it, she'll fire him from Team TARDIS, and directs him and Ryan to rescue the crew members instead of coming with her to find Tim Shaw, and solve the mystery of the item Andinio is demanding returned.
But just as Ryan tries to argue Graham out of his plan to murder Shaw, another callback from earlier in the season arrives, in the form of the Sniperbots from "The Ghost Monument." Yaz and Paltraki run into them too, as his memory slowly comes back. Meanwhile, the Doctor runs into Andinio and discovers she's a Ux, a rare spiritual species, who only ever exist in pairs and who now believe Tzim-Sha is their "creator." The Stenza has been directing her and her partner Delph (Percelle Ascott) to use their abilities to commit atrocities, to the point the Congress of the Nine sent Paltraki and others to put an end to it. All of this was to get the Doctor's attention so she would come to the planet where he's been trapped for 3,407 years since the adventure of Sheffield. It's a long con so he could get revenge. The object Paltraki has, and of which there are four more in the ship, are the planets which Tzim-Sha not only committed genocide against, but stole, and trapped inside these crystalline structures to turn them into the ultimate weapons. And now that the Doctor is here, he's going to trap Earth as his next target.
Graham: Yippie-ki-yay, Robots.
Graham and Ryan, unaware of the danger to Earth, go about freeing the hostages, accidentally catching Tzim-Sha's attention, and giving Graham his chance to kill the creature who murdered Grace. But when he gets the chance, he falters, having taken Ryan's words about being the better man to heart. In the end, he shoots our villain in the foot, just to shut him up. They stick him in one of his own crystalline prisons where the crew had been kept, trapped forever for his crimes in a stasis chamber of his own making. The Doctor, unsurprisingly, approves.
While Graham and Ryan have been stealing the show, the Doctor and Yaz convince the Ux that Tzim-Sha is no god. The Doctor summons the TARDIS, showing them Sha's "magical" appearance on their planet was not something only he can do. But mostly she just convinces Andinio she's a more powerful god to worship instead. Whatever, it's enough. Using the TARDIS, Delph and Andinio return the planets back to their correct places in space, with a small assist from Yaz and the Doctor, saving not only Earth but five other planets, which I assume includes Angstrom's homeworld from episode 2. Happy endings for all.
As the finale draws to a close, Paltraki loads up the survivors to get them home, and also agrees to ferry Delph to head out and explore the universe. Before Delph leaves, the Ux seal Tzim-Sha in his own ship, with Andinio to stand guard, protecting the world from the last of the Stenza. Team TARDIS head out again, ready to take on a new year's day episode and Season 12 come 2020.