This episode takes place across two distinct settings: the American 1860s Zone and central control. And in both the TARDIS team are fomenting rebellion and organising alliances to take on the sinister aliens behind the war games. Frazer Hines gets the best material he’s had all season, convincing the pith-helmeted Russell, leader of the resistance, to hijack a SIDRAT (which we learn are green) to travel to the enemy HQ. Meanwhile, the Doctor runs rings around the Chief Scientist, deprogramms Carstairs, rescues Zoe and plans to travel back out to the various war zones to unite the various bands of resistance soldiers.

The third strand introduced in this episode is the mutual antipathy between the War Chief and the Security Chief (the ever-constipated James Bree). Firing off accusations of incompetence and treachery, the two seem locked in a struggle for the approval of the unseen War Lord. The Security Chief has noticed the War Chief’s recognition of the Doctor; has learned about the TARDIS from Zoe, and has started to form suspicions about the War Chief’s motives, believing that he and the Doctor are of the same mysterious race, and wondering out loud where the War Chief’s loyalties really lie. Squabbling villains aren’t a rarity in Season Six – the Dominators, Vaughn and the Cyber-Planner and the Space Pirates all spent most of their time arguing with each other – but here it feels more like genuine hatred.

It’s a slightly odd move to include two races of aliens that look exactly like humans, but there’s a clever attempt to distinguish them by their accessories. The warmonger aliens all wear glasses or some sort of fancy eyewear, whereas the War Chief waves his shiny medallion threateningly, as if it confers on him special knowledge about space and time. Maybe it’s the Seal of Omega or something. Overall, Roger Cheveley’s set designs are also really impressive: the central control looks like something from a particularly groovy episode of The Avengers, with black and white stripes and strange semi-transparent hangings.

This is another pretty serious episode: a brainwashed Carstairs tries to shoot Zoe and only fails because his gun ran out fighting the Americans last week. And there’s a Star Trek style wrestling match between Harper and Spencer that goes on for ages. Troughton, though, continues to find ways to wring some fun out of it, particularly when he’s quizzing the Chief Scientist to discover that Zoe’s been captured and declares ‘Oh good!’ as he pulls a face that says exactly the opposite.

Next episode: The War Games: Episode Six