In some ways, this final episode feels like an inevitable outcome. Obviously things would have to go back to some form of normality, but it's a credit to the show that it didn't automatically feel like a foregone conclusion -- and they do provide a bit of leeway, rather than definitively shutting the door.
Hold on, let's back up a bit.
So after Salt escaped at the end of last episode, Barclay's been in protective custody and Aquakind has started melting the polar ice caps so they can drown humanity and turn the world into ocean. "You have five years [to clean up the world]," the new ambassador, Tide, tells humanity, "or all the water of the world will be set free. And be certain of this. Little people. This was never a war. This was an inconvenience. You were the dirt that gathered while we were away. But now we have returned, and you will be cleansed." So with that threat hanging over everyone's heads, Kate chooses to go to the Prime Minister to ask him about Severance. "I can help," she tells him. "There's always a way out. I can find it for you." But rather than convince him to accept Kate's help, this move instead pushes him to enact Severance -- which apparently involves injecting Barclay with some substance (and spraying his face with something) and then letting him out of his room to try and find Salt. Which he does, inadvertently infecting her with a virus that spreads throughout Homo aqua, killing off 90% of the population.
So yes, as I said at the top, it's a tribute to the show that this doesn't feel inevitable. You're often left wondering if there will be a peaceful resolution, and the show initially fakes the audience out when Salt seems to provide one: "Send out a signal to the seas, ask them for accord, and we might survive. All of us," she tells Barclay. We get a nice little scene where they figure out how to do it, and initially it seems like it might work, but it turns out it's already too late; the virus has already done its work. It's an effective pump fake. But, as with "The Hungry Earth"/"Cold Blood" (and the 20th-century Silurian/Sea Devil stories, to an extent), we see that ultimately it's humanity's violent nature that wins out. The villains, in this case, win. It leads to an emotional meeting between Barclay and Salt in front of the world, as she informs humanity that they've won. And when Barclay, per Kate's request, offers Aquakind a particular area to live, Salt bitterly calls it a "hunting ground" for humans to kill them, while it's not too hard to draw parallels to the way Native Americans were forced onto reservations by the American government. Definitely something of a downbeat ending then.
It's not completely downbeat though; sure, most of Aquakind was murdered by humanity (specifically the British Prime Minister and the two generals, who we see killed (maybe? It's not clear if this is the future or just imagined) by vomiting water and drowning inside a parked car, respectively), but at least Salt is still alive. And we learn that the reason Barclay has been having neck pain is because he's actually growing gills for some reason (I think this may have something to do with the accord, but if they actually explained it I missed it) and is now much like Salt, able to live both on the land and in the sea. So at least they get to end up together, with Kate sending them off. It's not a big triumphant ending, but it's at least something.
Except then after the credits start to roll they do the equivalent of an MCU post-credits scene, with a jogger tossing aside a drink bottle and Kate asking him to pick it up, which escalates to her holding him at gunpoint and demanding he pick the bottle up. (Which is definitely extreme, of course, but also, my guy, you just lived through the planet getting pelting with trash and almost getting wiped out because of humanity's pollution and littering, so why the hell are you still tossing bottles aside on the beach instead of putting it in a bin?) It looks like the stress has finally gotten to Kate Lethbridge-Stewart, and this is her cracking.
That may look like a tease for the future, but we're not going to get any sort of follow-up anytime soon, if ever. The War Between the Land and the Sea did OK critically, but ratings weren't anything special -- basically the same as the most recent series of Doctor Who. In some ways that's a shame; while this wasn't the best show (or even Who spin-off) ever, it was still solid, and it showed that there is indeed some merit to the idea of a UNIT-focused show. Russell Tovey, Gugu Mbatha-Raw, and Jemma Redgrave all deserve praise for their performances, and they were aided by an excellent supporting cast, with Cat Gannon as Kirby, Ruth Madeley as Shirley, and Francesca Corney as Sgt. Hana just some of the many great actors seen here. Other than some unresolved questions, the scripting was also good (and writing-wise, this final episode was leagues ahead of "The Reality War" or "Empire of Death"). It's frankly a little surprising that, in the United States at least, Disney still haven't released this yet. It's nothing embarrassing and honestly there's no reason it couldn't just be quietly released on Disney+ without a lot of fanfare, like any number of other shows on the platform (or even Doctor Who itself, to an extent). The War Between the Land and the Sea is a generally enjoyable story, even if it's not the flashiest thing ever.
But that, perhaps surprisingly, may be the final word on Doctor Who on television for some time to come.309 After Disney officially announced they weren't renewing their agreement with the BBC, a Christmas special was announced, but as time passed and nothing happened on the front it became clear that this wasn't going to happen, and eventually the BBC cancelled it in June 2026, with Russell T Davies/Bad Wolf Ltd. officially stepping down from making the show (and Davies stating he'd never even written a script for the special). The BBC don't seem to want the show to just go away, the way they did in 1989, since they officially began the process in September of finding another production partner for the show, opening it up to companies to bid for. But even if anything comes of that, it will still take time for a new series to start moving. The Doctor, it seems, is on another break. Let's just hope this one is shorter than 16 years.
309 Unless you count this animated Doctor Who: TARDIS Crew show aimed at preschoolers that's coming out on CBeebies (the dedicated BBC channel for ages 5 and under) sometime in the next year or two. Maybe I'll cover it, but the teaser image that's been released so far makes this look like little more than a fun and silly way to entertain young kids, and not anything intended for a larger audience.