This one sets the scene for most of the early ‘space’ adventures. Whereas the history stories usually begin with the crew being captured and separated in fairly short order, the space adventures take a bit more time to explore the environment. The Dead Planet is particularly memorable because of the effort that’s gone in to making the planet so alien. The petrified jungle is stark, with weird, rectangular leaves – quite a difference from the prehistoric Earth forest last week. It’s also shot with a weird ‘negative’ effect, at least for the first 30 seconds, which makes it look as strange as Vortis, and creates a link between the dead planet and the Daleks’ death ray effect.

The other alien environment is the city. The initial reveal is quite a neat effect, managing to incorporate the time travellers into the model shot. After that, Christopher Barry shoots it like it’s something from a 1980s horror film: slow pans into the fog-wreathed city accompanied by a low, ominous bass sting. Once the time travellers get into the city, Barry incorporates Dutch tilts to make it look unsettling, and emphasises that something is watching Barbara with cameras turning as she goes past. She puts her hand over the camera at one point, and then the cliffhanger is shot from the monster’s point of view.

Against this alien-ness is the sudden domesticity of the Ship, which four weeks ago was a frightening environment. Now, Ian and Barbara are starting to treat it as a home from home, enjoying the food machine, and talking sleeping arrangements with Susan. Even the Doctor is softening a bit: he’s still tetchy and confrontational, but he also gets his first comedy scene with Ian as he’s checking the computer banks. He’s gone from slightly threatening to mercurial – a point emphasised by his fiddling with the mercury fluid links to get his own way. He’s a risk to the rest of the crew not because of malice, but because he’s unpredictable.

Hartnell isn’t at his best in this episode, though: he gets his first fluff a couple of minutes in when he stumbles over the explanation of the metal creature’s magnetic field, and he stumbles over another couple of lines inside the TARDIS. Maybe it’s because they had to re-record this one later without much time to prepare? They should have taken the opportunity to address the most obvious problem with the episode: the time travellers go back to the TARDIS twice during the episode, the Doctor checks the computers, Susan checks the fault locator, but no-one notices that the radiation detector is either flashing or else broken down.

Next episode: The Survivors