The Doctor and her companions receive nine separate distress calls, all originating from the mysterious planet of Ranskoor Av Kolos, which turns out to have been the site of a terrible battle. As further secrets are uncovered and strange forces gather in the mists, the only clue to what has happened on this world is a commander who has no memory.

Mark Addy guest stars alongside Jodie Whittaker in the final episode of her debut series. The Doctor will return for a special episode on New Year's Day. Last in the series.

(From Radio Times)