Most of this episode focuses on the burgeoning crisis in the colony. While Governor Hensell sets off for a tour of the perimeter, Bragen’s plot to discredit Deputy Quinn succeeds and propels him to be the Acting Governor in Hensell’s absence. At this point, it transpires that Bragen essentially has the same plan as Chancellor Palpatine in the Star Wars prequels. The ‘rebels’ have been secretly cultivated by him as a threat that he will sweep in to defeat, to much popular acclaim and the certainty of winning the office of Governor. Which makes Janley the Count Dooku character – ostensibly the rebel leader, but actually Bragen’s partner in crime.

While the colonists’ power play unfolds, the Doctor and Ben know the real danger are the Daleks. Troughton’s portrayal comes into its own here: where Hartnell would have tried to take command, and made the most of his purloined credentials, the second Doctor looks like a raving madman when he demands the Daleks are destroyed. Instead, he decides to act more covertly, trying to sabotage the Dalek power supply, and, in a brilliant scene, confessing to Bragen – who he has deduced killed the real Examiner – that he is an impostor, but banking on Bragen’s uncertain power base to buy him more time to end the Dalek menace.

For the bulk of the episode Ben and Polly become an audience for the new Doctor, watching him leap about dismantling bits of set and lashing up a gadget to disable the Daleks. The telesnaps show Craze laughing at Troughton’s physical comedy. Along with this nervy physicality comes a stream of consciousness thought process, as he explains to Polly how he needs to tackle Lesterson. You just can’t imagine Hartnell doing this much stuff, especially in his final series.

Just as the Doctor prefers to act behind the scenes, so the Daleks are more manipulative than ever – guiding Lesterson to get them the materials they need, while all the time pretending to be subservient. But there’s a great moment where a disarmed Dalek’s gun socket clicks impotently in frustration after the Doctor riles it, and brilliantly, for the first time the classic second Doctor line…

THE DOCTOR: When I say run – run like a rabbit… Run!

Next episode: The Power of the Daleks – Episode Four