While I’m not planning to go into a lot of plot details, it’s likely that the random mutterings that follow will reveal some things you might prefer not to know if you haven’t seen the episode yet, so in my usual way, I’ll include this warning:
Ooooookay….. Now that had some serious wibbly-wobbly timey wimeyness about it. Now the first part seemed normal enough. The Doctor and Clara arrive at an underwater base where things are definitely not quite as they should be, what with the homicidal ghosts of dead crew members appearing every time the base goes into night mode. Yup, traditional base under siege stuff. And equally traditionally, it all seems to have started when they brought an alien vessel on board. Realising that the only way to sort it out was to go back to before the lake was created by flooding, the Doctor is obliged to leave Clara behind.
Things start getting strange when the ghosts are joined by a new one: the Doctor, which is as nicely cliffhangery as you can get.
And then the second part stated with a curious bit of stuff in which the Doctor, speaking to camera, posits a hypothetical situation in which a time traveller goes back to meet Beethoven only to find he doesn’t exist, so publishes handwritten copies of all the Beethoven scores he’s conveniently got with him, thus bringing Beethoven’s work into being, leaving the question “who wrote Beethoven’s Fifth?” hanging nicely as he brings out the guitar again….
And so the wibbly wobbliness continues, with Clara and some survivors trying not go be killed on the base, and the Doctor dealing with a particularly ruthless alien known as the Fisher King. There’s also the slight issue of potential paradoxes, which upset the Tardis so much that the Cloister Bell rings, and the Doctor finds he can’t make a trip he was planning, so has to think of something else.
Lots of running around is involved, as is much confusion, which will probably require watching these episodes again with extreme use of the pause and rewind buttons.
And yes, there is a lingering paradox at the end, which feeds back into the question asked at the beginning of the second part.
Wild. Lots of fun, but distinctly confusing. Which isn’t a bad thing as far as I’m concerned. Time travel should cause a fair bit of oddness, and it’s nice to see that being embraced more.