The first half of this episode picks up where The Escape left off. It’s exactly the kind of thing we’re going to see a lot of in the future with the regulars pretending to be prisoners, and the baddies cutting through doors with blowtorches. It’s done reasonably well, but it’s very routine and mainly noteworthy because the Daleks start using ‘exterminate!’ as a catchphrase.

The Ambush only gets interesting when the Thals enter the Dalek city. Temmosus is portrayed as a noble man, but one whose ideals cannot stand against the Daleks’ ‘dislike for the unlike’. The Thals are implicitly like the ‘guilty men’ of the 1930s, scarred by the memories of the last war against the Dals and unwilling to fight again. The ambush itself is a fantastic sequence, played almost without dialogue, and with Tristram Cary’s ominous, low note repeating dolefully as the Daleks slide in unison into their hiding places and Temmosus walks towards his fate. Then, as Temmosus makes his appeal, the Daleks creep towards him and brutally murder him. As the other Thals and Ian escape, there’s a great special effect of a wall bubbling and melting behind Ian. It’s the most visually impressive sequence so far in the series.

The last part of the episode is set back at the Thal camp. Ian recognises Temmosus’ good intentions, but, pragmatic as ever, he believes that pacifist principles are worthless when not shared by your enemies. Meanwhile, the Doctor discovers both the name of the planet – Skaro – and more about Skaroene history: the neutron war, the mutations and the martial history of the Thals. But, unlike Ian, he’s only academically interested. He has no desire to get involved. This continues a conflict between the two men that was set up in The Survivors, where the Doctor is impressed by the Daleks’ intelligence, but Ian is more concerned with the use to which that intelligence is put. The Doctor at this point is amoral: to him, intelligence has nothing to do with ‘right’ or ‘wrong’, whereas to Ian it’s the practical, moral use of it that counts. The end of this episode suddenly makes this disagreement very pertinent, because the mercury fluid link is still inside the Dalek city, and it seems quite likely that the time travellers will need the Thals’ help if they’re going to escape.

Next episode: The Expedition