‘The future lies this way.’ One remembered for its atmosphere and tone rather than some of the shonky details (it seems unlikely the chameleon circuit works by having to land somewhere and measure something in detail before imitating it). There’s a curious resignation to all of this: even before he sees himself, the Doctor seems haunted, disturbed by the possibility that the Master is hunting him, morose about the reception that awaits him on Gallifrey. He misses Romana (who, brilliantly, had a photo of K9 next to her bed), and is unusually chatty about his past (‘there were rather pressing reasons’ for taking the TARDIS from the repair shop on Gallifrey, apparently). With the ululating, eerie Paddy Kingsland score and the TARDIS a dark and sinister space for the first time since Death to the Daleks, it’s very effective.

The lightness is provided by Tegan Jovanka and Auntie Vanessa. Some of these scenes over-egg Tegan’s backstory, and it’s hard to believe she’d grasp that the TARDIS is a craft with a pilot just from wandering into the control room, but largely it all works as comedy, and a way to establish Tegan’s self-reliance undercut by the likeable ditziness of her forgetting her bag, to close the door and so on. It’s the most elaborate introduction of a new companion since Sarah Jane (and, coincidentally, also involves an aunt), although I’m intrigued by the possibility of Vanessa heading into the phone box instead.

There are some impressive visuals: the witty opening shot of what looks like the TARDIS revealed to be a real Police Box; the Russian Doll of TARDISes and the crumbling cloisters are somewhat reminiscent of the strange spaces in Warriors’ Gate, and the December location work is suitably chilly. It creates a bit of a link back to the start of the season (the last time we saw the Doctor on Earth, on a similarly bleak-looking Brighton beach), made creepy by the wordless, deathly presence of the Watcher. This is as good a hook as any in Season 18.

Next episode: Logopolis – Part Two