This is the first Doctor Who episode to actually utilise colour for effect: when the Doctor is taken aboard the UFO to meet the captive human astronauts, he’s lit by bursts of pink, green and blue light. It’s a marked contrast after the wintry greys and muted shades of the space centre. Later, Liz comes literally face to face with one of the alien ambassadors and Michael Ferguson uses a strange repeated zoom as the alien removes its helmet to reveal a lumpy and bright blue face.

These are standout moments in a story which casts human beings as the villains and the aliens as innocent victims. The title is revealed as more than schlock horror – the three alien astronauts are actually ambassadors, but humankind has treated them like monsters. Coming straight after Doctor Who and the Silurians tried to take a more even-handed approach to its monsters, this Twilight Zone morality tale enhances Season Seven’s reputation for being more nuanced than the series has been for several years. Maybe the Time Lords didn’t just send the Doctor to Earth to protect the planet from aliens, but also to protect aliens from human beings.

Also following on from Doctor Who and the Silurians, the Brigadier is again confronted with a choice to go on the offensive against the UFO in orbit, or to take a more measured approach. His response belies the cheap “the Brigadier’s a murderer!” jibe, as he’s willing to consider a military response, but prefers to learn more about the potential threat first. His treatment of the genocidal Silurians was fair enough, but he’s not bloodthirsty. By way of contrast, General Carrington immediately goes to the UN to try to get the ship blasted out of orbit as his conspiracy unravels around him. Reegan has abandoned any pretence of following Carrington’s orders: in a glorious lack of imagination he plans to use his alien captives to rob banks, and co-opts the Doctor to help. This involves knocking him out, and giving us our first glimpse of the classic “Pertwee Death Pose” and a touching moment with Liz that almost exactly mirrors his very last moments with Sarah Jane.

I’m really enjoying how the story is developing quite methodically – as you might expect from an (uncredited) collaboration between Malcolm Hulke and Terrance Dicks. But there are some weird choices, like Lennox dying and the Brigadier finding out offscreen and then just dropping it into conversation. But maybe he’s just feeling sheepish given how easily saboteurs seem to be able to wander in and out of Space Control. It’s not a great look when Reegan’s thugs offer better security than UNIT.

Next episode: The Ambassadors of Death – Episode 7