"Thin Ice" is the third episode of the tenth series of the British science fiction television series Doctor Who. It was written by Sarah Dollard and broadcast on 29 April 2017 on BBC One. "Thin Ice" received mostly positive reviews from critics, with many labelling the topic of racism in the episode as well-executed. The Doctor (Peter Capaldi) and Bill Potts (Pearl Mackie) visit the last great frost fair in London 1814, but they soon find that something sinister is lurking below the frozen Thames.