After last week’s grim horror, this is a marked change in tone. The Doctor and Steven don’t even realise Vyon has been killed until Sara tells them much later in the episode. Instead, they – and Sara – are caught up in a matter transmission experiment that beams them and some mice halfway across the galaxy courtesy of a rather horrible solarising effect that turns Hartnell’s face into a gurning skull. Sadly, though, we’re denied him trampolining through space on the way to the distant destination.

There’s a fine balance to this episode, which could easily be called Counter Point. The scientists Froyn – a very serious, cross man – and his co-worker Rhynmal, who’s as camp as Christmas and played like a Charles Hawtrey character are quite good value. But even better are Chen and Karlton, whose relationship is fascinating: Chen, slightly insane, veering from grandiloquent megolamania to utter despair when he thinks he has lost the Taranum; Karlton, seeking to weasel out of the problem with cunning plans, while giving the impression that he’s using Chen as the charismatic front for his own power games. Maurice Browning is brilliant as the plotting functionary. And Kevin Stoney pushes Chen up to 11, introducing little details like his habit of pointing or scratching with his little finger, and rolling his eyes up as he dreams of galactic conquest.

Across the universe, the steaming jungle planet Mira (an obvious precursor to Spiridon, especially with its similar name and invisible inhabitants) is one of the most impressive alien planets yet seen – drifting smoke, bubbling water, dense vegetation. Trapped there, the Doctor and Steven try to convince Sara of their honesty (although it takes the Daleks’ arrival to confirm the truth), and in turn she reveals that Vyon was her brother. Jean Marsh and Peter Purves sizzle in their scenes together – it’s no wonder later writers have seized on this relationship. The episode ends with one of the most dramatic cliffhangers – cornered by the Daleks, the Doctor tells Steven, Sara and the viewers, ‘I’m afraid, my friends, the Daleks have won…’

Next episode: Coronas of the Sun