I see Pete McTighe has taken over the writing duties for this episode (and the next two). That's perhaps appropriate, given that one of the Doctor Who episodes he (co-)wrote was series 12's "Praxeus", which was about plastic pollution and is in some ways a sister episode to "Plastic Apocalypse".
This is, perhaps unsurprisingly, another fairly talky episode. The primary focus is on Barclay's new position as ambassador, dealing with all the political juggling among many nations as he tries not to screw things up. And while we get a couple early series of Barclay being sternly questioned by Kate Lethbridge-Stewart ("What communication have you had with with Homo aqua prior to today?" Kate demands. "None, never," Barclay responds. "I had a goldfish once, is that relevant?" he adds. "This isn't a joke, Mr Dupont," Kate says sternly. "I wasn't joking," Barclay says quietly. "His name was Simon"), fortunately we don't spend too much time questioning Barclay's background and allegiance. We do get a nice scene between Barclay and Kate in the back of a van, where she can let down her front with him a bit, though: "Barclay, I need someone I can work with," she tells me. "And I think I can work with you."
But it still feels like a fair amount of setup is happening in this episode. This is where the initial negotiations between humanity and Homo aqua begin, but we only get a couple sessions, both of which are controlled by the Homo aqua's ambassador, Salt, despite humanity (aka Kate)'s best efforts. Salt is played by another familiar Who veteran: Gugu Mbatha-Raw, who played Martha's sister Tish back in 2007. She, like Russell Tovey, also does a good job of staying engaging (no mean feat under that makeup), and you kind of wish we could get more scenes of her and Barclay talking, since they're both compelling performers. Salt is obviously the aggrieved party, dealing with all the pollution that humanity has been pumping into the oceans, so that means she has to be a lot more severe and solemn than Barclay. Barclay is doing the best he can, and while the moments where he goes off-script are fun ("This is like working with the Doctor," Kate grumbles), he also does a good job of sticking to the script and trying to negotiate in good faith with Salt and not assuming that he knows better. It's kind of refreshing, to be honest, to be provided a protagonist who doesn't automatically assume he knows what's best and has it blow up in his face, the way you could see the American version of this series going. Instead we get someone who seems reasonably competent and only sometimes speaks his mind. It's a good balance.
That said, there are still a couple odd moments. The titular apocalypse comes after Salt basically does a "are you sure that's what you want? OK then" rugpull and sends all the trash from the oceans onto the land. And while it looks dangerous and all falling from the sky (theoretically, at least; I'm not convinced they really sell this the way they're hoping to), it also doesn't look like that much? I was sort of expecting literal mountains of trash, not just a couple feet of it. I'm sure it damaged a bunch of stuff falling from the sky (another thing that isn't remotely explained how), but it also doesn't look that apocalyptic. It'll be a pain to clean up, but not insurmountable. I can see why it would upset humanity and make them scared, as Barclay states, but it seems like it could have been worse.
There's also a short scene (with no closure, so I'm sure we'll see them again in future episodes) with a British oil baron, an American general, and a French general where they plot against peace in such cartoonishly evil ways that they might as well wear signs saying "Villain". There's probably a point to be made about how people with financial investments and short-sightedness are going to working against some sort of treaty if it means they have to stop polluting, but this isn't it. They sit around cackling and eating fish and caviar to ram home the point that these are Bad People and you kind of wish they'd just go away; we're a long way away from the nuance of a Malcolm Hulke308 character here.
Don't get me wrong, there are some good moments in "Plastic Apocalypse", such as Barclay's interaction with his teenager Kirby, where we see that they have a nice loving relationship, or the way we see that the relationship between Kate and Colonel Ibrahim has actually developed, and the interactions between Salt and Barclay are also worth watching. But so far this series has been more interested in talking, and while Tovey and Mbatha-Raw do a great job with this (not to belittle people like Jemma Redgrave, of course, who are also doing a great job), now that we're getting to the halfway point here, it's time for some action. Let's hope "The Deep" can start to deliver.
308 The writer of Doctor Who and the Silurians and The Sea Devils, if you've forgotten.