“Before the Flood” is episode four of season nine of the new Doctor Who.
At the end of the previous episode, “Under the Lake”, the Doctor had decided to go back in time to when the spaceship crashed. Those still left in 2119, which includes Clara, then saw the Doctor’s ghost – so it seems that he had died in the past.
This episode begins with the Doctor giving a lecture about the Bootstrap Paradox (which caused a spike in searches for the term at the time). Whilst this may have been interesting, it didn’t seem relevant at the time – it was only later that it did.
The Doctor has gone back to when the spaceship landed, back in 1980, before the town was flooded. It looks like a Soviet town, but this was the height of the Cold War, and it was a training facility.
The spaceship’s pilot is still alive. He’s an undertaker, and the craft is a hearse, transporting a supposedly dead – but not, it seems, dead enough – warlord called the Fisher King.
Can the Doctor save himself and Clara? He’s supposedly already dead, and he doesn’t want to change the future. It does all seem to work out logically enough.