In the end, right until the last couple of scenes, this is a bit of a disappointment. There’s some drama around the Doctor having been kidnapped before he can reveal the formula for the cure to the plague, until Liz finds it written down on a bit of paper. Then, to create some drama for the final episode, the Silurians reveal they have another genocidal plan – to use a gizmo to remove the Van Allen Belt and roast humankind – that can only be foiled by the Doctor fusing the control of the neutron flow in the cyclotron.

This all keeps things going for 25 minutes, but it’s a lot less interesting than the last six weeks, and it makes the Silurians seem less like the ‘intelligent alien beings’ the Doctor describes and more like a bunch of belligerent, mass-murdering monsters. All this tends to make the Doctor’s keenness to go back down into the caves to begin reviving more of them look like madness, and the Brigadier’s response – which is described as sealing the base rather than blowing it up – sensible. The Doctor’s horrified reaction is a great moment (as is Courtney’s stony-faced reaction in their final exchange of the episode) but a bit naive in context.

Still, the downbeat conclusion, and Liz’s scornful reference to ‘the government’, are something different. Other than the departure of regulars we haven’t really had an unhappy ending since The Massacre, and it’s pleasing that Season Seven isn’t just aiming to be “Doctor Who in colour!” but also making its stories a bit less morally black and white than they had been during the previous few years. The longer serial has been used to make some of the characters a bit more nuanced rather than just trying to introduce more incident, and it’s obviously helped the budget given the number of Silurians involved in the final attack, and the scale of some of the film sequences. I hope they can keep it up.

Next episode: The Ambassadors of Death