DRAMA London, 1814: a vast mud-caked creature wails in anguish down by the Thames... No, it's not Tom Hardy returning unexpectedly early as James Keziah Delaney in Taboo. We are in the exact same year and setting, but Doctor Who delivers a far less squallid depiction of Regency London - its street urchins are quite well turned out.

The Doctor and Bill arrive at the last of the great frost fairs on the Thames, where revellers and children have been vanishing under the ice. There are monsters at large - if not the kind we first imagine. "Regency England is a bit more black than they show in the movies," observes Bill, wary that in this period "slavery is still totally a thing". Indeed, undercurrents of bondage, racism and inhumanity soon bubble to the surface.

Thin Ice is a superb episode, written by Sarah Dollard, in which Bill asks questions that cut to the core of the Doctor's morality. Pearl Mackie is a remarkably empathic prescence, while Peter Capaldi is the finest he's ever been at the wit, fury and remoteness of the Time Lord.