Patrick Troughton’s debut story is full of memorable moments: the opening to episode 1 in the immediate aftermath of the transformation; the Dalek recognising the Doctor; and Lesterson’s mental collapse, to name just a few.

My chosen moment comes early in Part 2 as the new Doctor starts to take control of the situation. Accompanied by Ben and Polly, he’s managed to open the mysterious capsule containing the deactivated Daleks. Confronted by a furious Lesterson (“I should have been asked first!”), the Doctor reveals that the scientist has been lying – he’d already found the Daleks and has concealed one for testing.

Lesterson, played by Robert James in one of the all-time great Doctor Who guest performances, complacently dismisses any risk (“Lumps of metal, quite inactive…”) and the Doctor, posing as the Earth examiner, demands to see the governor.

Left alone in his laboratory, Lesterson covets his hidden Dalek: “There must be some way to bring you back to life, and I’m going to find it!”

I love how the scene works on different levels. Lesterson is exposed as a liar, and begins to reveal his obsessiveness, but it’s possible to sympathise with his outrage that the Doctor (who, after all, tells a pretty big lie of his own when he brandishes the examiner’s badge) has been snooping around the laboratory.

Most of all, there’s the atmosphere of foreboding that pervades the scene, and indeed the whole story. The Doctor knows, as does the viewer, that everyone on the base is in the most terrible danger, and that Lesterson’s quest for knowledge will surely be the undoing of them all…