"So, we are fighting an unknown homicidal force that has taken the form of your commanding officer and a cowardly alien, underwater, in a nuclear reactor. Anything else I should know? Someone got a peanut allergy or something?"
IN THIS ONE... An underwater base is plagued by killer radio ghosts.
REVIEW: Modern Who's base under siege stories all kind of look the same, and Under the Lake poaches liberally from The Impossible Planet, but Toby Whithouse's remix of those ideas keeps us and the Doctor guessing, which is part and parcel of why I champion him to be the next showrunner. This episode is, on the surface (pun not intended), just another monster story, but it keeps twisting in on itself. And many of those twists are the Doctor's own work! After dismissing the idea that they monsters are ghosts, he decides they ARE ghosts. When the crew has a means to escape, he decides that's what the ghosts want and so it shouldn't happen. When the lights come on, making everyone safe, the Doctor has them shut off again so they can learn more. Curiosity is what solves the problems, but it's also what causes them, as everyone gets infected with alien writing. In a story where characters die and start to act against their friends, it makes some kind of sense that even in life, they would act self-destructively. So the crew agrees to stay even when the Doctor tells them they should go, but then, he makes staying sound so appetizing. And he would rather Clara stay safe, but her thrillseeking has become a problem, a refuge from her grief. The stand-out scene of the episode has her hold back the tears as the Doctor warns her not to "go native" inside the TARDIS and turn into another version of him.
There is some great characterization all around, in fact. Clara's flippancy and borderline death wish are developed, but this is also the 12th Doctor at his giddiest, his head spinning with possibilities and impossibilities. Giddy, but no less irascible, showing beautiful contempt for the 70s-style bureaucrat in charge, his impatience at how slow everyone is compared to him, and his Siskoid-like refusal to give high fives. Clara-as-teacher plays a part thanks to some hilarious flash cards she's made for the Doctor so he can express proper emotions and tolerance (my favorite definitely the one meant for Sarah Jane Smith at the end of The Hand of Fear). And even among the guest crew, the characters are well delineated archetypes, with the deaf commander Cass (played by truly deaf actress Sophie Stone) and her interpreter, Lunn, struggling to follow the Doctor's words, a highlight. Obviously, her ability to read lips figures into the plot, but she's a better drawn character than most even without that function. Her fear and courage both feel real, and she's far more able to stand up to the Doctor than those who hear his voice.
Whithouse even manages to cover for his story's main weakness - how quickly the Doctor interprets the message transmitted by all these hijacked souls - with dialog about an earworm infection, the words (and possibly their meaning, for someone as clever as the Doctor) already implanted and rewriting everyone's brains (except for Lunn's, who has yet to see the magic words). Well, okay, the Clara hologram apparently beamed in with the sonic glasses' wi-fi is something of a cheat too, and probably what we were all thinking the cliffhanger was. The Doctor prefigures his going back in time to the flooded location by saying he had to go back to the beginning of his investigation, but the promise of a timey-wimey resolution brings unexpected joy.
REWATCHABILITY: Medium-High - The set-up lacks originality, but the execution features some generally excellent plotting and characterization.