Most of the opening episodes of the sci-fi adventures are relatively eerie – from the exploration of the Dead Planet Skaro and the horrors of Marinus, to the spaceship tomb of The Sensorites and the weird surface of Vortis. This one’s pretty great though. The TARDIS has landed in amongst a whole load of rocket ships in a space museum. But straight away there’s something not right – the regulars aren’t wearing the same clothes as last week, and then a dropped glass reassembles itself in Vicki’s hand.

There are some great ideas here. The concept of being out of sync with the rest of the world – not leaving a footprint in the sand, unable to touch the museum exhibits or communicate with anyone else – means that the TARDIS crew have become ghosts from their own futures. There’s a sense of mounting unease from a very low baseline – the Doctor’s total unconcern about suddenly wearing different clothes is handled as a joke when it ought to have been unsettling. But even this works because as the evidence that something is very wrong mounts, the Doctor’s transition from hand-waving good humour to troubled frown, to grim-faced horror maps a neat trajectory for the episode. The climax – seeing their own corpses stuffed and mounted in the museum – is probably the most horrible scene in the series so far, and it’s a superbly haunting image.

Sadly, the last few minutes rely far too much on Hartnell being able to make sense of a not very articulate script. There’s some waffle about the dimensions of time and jumping a time track, but it all comes across as slightly baffling nonsense. The layman’s explanation – ‘What we are doing now is taking a glimpse into the future, or what might be or could be the future. All that leads up to it, is still yet to come’ – is a bit lost among the confused chatter. This means that a potentially compelling danger – can the future, once foreseen, be averted? – isn’t as well established as it needs to be. Which is a shame, because the idea is strong and it’s a neat counterpoint to The Aztecs’ ‘You can’t change history’ problem. Can you change history if you’ve become part of it?

This feels like a critical weakness in an episode which to that point has been filled with fantastic image and scenes. Having the regulars come face to face with a Dalek – also reduced to a Space Museum exhibit – is clever because it suggests whoever created the museum must be a formidable danger if they’re able to reduce the Doctor’s arch enemies to items of idle curiosity. It also gives Vicki a chance to once again establish she’s from the far future, when the Daleks were something from the history books. This is further reinforced when the TARDIS itself is reduced to an inaccessible ghost, removing any chance of escape.

Amusingly, the episode concludes with what’s essentially a telesnap reconstruction of the adventure so far, as time catches up with the crew. The mummified regulars vanish, and the Doctor announces ominously, ‘We’ve arrived.’

Next episode: The Dimensions of Time