N.B. there might (or might not) be spoilers in this article!

While it isn’t exactly Threads, a post-apocalyptic Britain in which Donna doesn’t meet the Doctor is certainly a grim ‘un.

“Turn right, and never meet that man. Turn right, and change the world.”

Fortune Teller, Turn Left

It’s a traumatic one for the fan too – here presented with the off-screen deaths of Martha Jones, Sarah Jane Smith and her teenage crew and Cap’n Jack’s Torchwood team in this parallel world that only exists if Donna turns right and chooses a job with Mr Chowdry.

It’s also the second episode in a row where we get to see how humans behave in panic mode. Whereas Midnight‘s terror was small-scale and claustrophobic, in Turn Left, the human capacity for cruelty when afraid is writ large – with the treatment of Rocco and his family – shipping them off to “labour camps” now it’s an “England for the English” bleak fare for a Saturday tea-time show.

“You’re not going to make the world any better by shouting at it.”

Wilf, Turn Left

You have to give him his due: Russell the Davies can bite when the mood takes.

In the absence of the Doctor, Donna becomes Doctor Who‘s star for the week – ably supported by her Mum and Grandad. We’ve come to expect excellence from Catherine Tate and Bernard Cribbins, but I was particularly impressed by Jacqueline King as the increasingly exhausted Sylvia Noble.

And, after teasing us for most of the season since that initial cameo, we finally get to see Rose Tyler again. The two-word message she passes on to the dying Donna-who-turned-right makes for a cracking cliffhanger to lead us into the season finale: Bad. Wolf.