Blimey, there’s a lot going on here. Both of Malcolm Hulke’s previous scripts have featured a realistic setting (airport, WW1 battlefield) infiltrated by something uncanny, and this continues in the same vein. The Wenley Moor research centre is TV realistic (all the very serious briefings and personnel problems – Major Baker, for instance, ‘slipped up badly once some years ago’), and feels very 1970s contemporary with its backdrop of energy crisis and atomic power. This is offset by the very dodgy-looking dinosaur lurking in the caves, and Spencer’s regression to a caveman state, which fits much more in the 1970s strand of the ‘return of the repressed’. It’s obvious the two plotlines are connected, but so far this doesn’t indicate how. If this were an ITC series the dinosaur would probably turn out to be a special effect to keep people away from the enemy agents’ base, but as this is Doctor Who it’s clearly going to be something alien.

There’s nothing here that we haven’t seen in some way before – new technology going slightly wrong was a feature of the first of the show’s contemporary plotlines, The War Machines, back in 1966 and more recently in The Seeds of Death. But we haven’t quite seen it handled like this – following the arrival of the Doctor, at the invitation of UNIT, to investigate as a paid consultant rather than stumbling into the middle of a crisis by accident. As such, there’s a bit more emphasis on procedure than normal – the Doctor’s investigation of the log books, for example – although again this is not a million miles from The Faceless Ones.

Pertwee looks quite comfortable in this setting, with little of the sense of finding the character that was obvious in the first couple of Troughton stories. True, he’s singing a whimsical tune when he first appears (which may be a hint of Sherwin and Bryant’s conception of the character as a guitar-strumming guru), but otherwise this is pretty much the character we’re going to get for the next five years. His relationship with the Brigadier is suddenly more antagonistic than last week, implying they’ve been working together for a while, although conversely he’s only just started tinkering with Bessie, the vintage car he was promised at the end of Spearhead from Space. He’s also far from delighted at being a member of the UNIT team – ‘depressing, isn’t it?’ But as soon as he’s presented with practical problems – like the power fluctuation in the cyclotron, or Spencer’s insanity – he immediately jumps in to help. So far this has given us some relatively familiar Doctor Who ideas that feel fresh because of the new Doctor and the new set-up.

But seriously – that dinosaur. What were they thinking?

Next episode: Doctor Who and the Silurians – Episode 2