Oh, hey, Sea Devils can talk!
Yes, it seems the Sea Devils can talk, and they don’t like humans. The Doctor was captured and taken to their undersea base where they’re planning humanity’s extinction because the planet used to be theirs but then they went into hibernation to avoid a catastrophe that never happened and their alarms didn’t go off to wake them up in order to either get to work on time or prevent the monkeys from evolving into humans. Now, the Doctor believes, once again, that he can negotiate a peace between humans and lizard people, and he might…but then the Master shows up to drop some truth bombs, namely that it didn’t work the last time the Doctor tried that with the Silurians. And yes, the Doctor admits he failed, but he can try again because while the Master keeps suggesting the Sea Devils can wipe out humanity very easily because humans are weak, the Doctor says they’re very good at blowing things up, so why not try the Doctor’s way? And that seems to be working with the Sea Devil leader…
…until some older, overweight official government minister, the kind that prefers to push people around rather than listen to more sensible people like Jo and Captain Hart–and you know you have problems the way this show is written if Jo comes across as smarter–and just orders some ships to drop depth charges onto the Sea Devil base despite the Doctor and potentially a submarine crew being down there…
You know, there sure are a lot of pompous windbag ministers messing things up on this show.
Point is, Sea Devils are a lot less inclined to go for peace when their undersea home starts getting bombed, and they opt to try the Master’s strategy for now. The Doctor is led away to be executed, but you know that won’t happen, especially when his guards are taken out by a collapsed section of the ceiling. That leads him to a prison cell where Young Maester Luwin is being held with his second in command, and that leads them to the World’s Roomiest Captured Sub, and the Doctor is able to guide the crew out, even getting past a forcefield with some handy torpedo explosions, and he only has to chastise Luwin once for shooting a Sea Devil on the deck.
As for the Royal Navy’s attack, it stops when the Sea Devils, under advice from the Master, let some debris and bodies float to the surface, making it look like the attack was successful. But the Master needs more parts to finish his wake-up-the-Sea-Devils machine, so that means they need to attack the Naval Base.
And so, once the Doctor has returned, realized Hart was not the officious idiot in charge of ruining his negotiations, and then gets no response from the officious and oblivious idiot who was, that means he needs to try again to arrange peace.
Problem: Sea Devils attack the base, and one of them soon gets the drop on Jo and the Doctor.