Two of the classic clip-compilation moments happen early in this episode. First, the Doctor hurls himself on barbed wire, and uses the sonic screwdriver to detonate a minefield to scare off a pursuing Sea Devil (probably best not to ask why he didn’t just blow up all the mines straight away rather than than creeping slowly through them). Later, in a bigger and better repeat of the previous cliffhanger, a host of Sea Devils rise from the sea, at dusk, to attack the castle.

These are typical of a serial that’s doing something memorable in every episode. This brings the Master’s alliance with Trenchard to an end as Trenchard’s rapidly increasing suspicions about the Master’s motives result in the old duffer dying in a final display of bravery. When the Doctor and Hart find Trenchard’s body, there’s a moment that really hits home how, despite how fun he can seem, what a nasty piece of work is the Master. Trenchard’s defining quality was patriotism and a love of country that the Master twisted into something he could use to destroy the foolish but rather amiable old man.

Hulke balances the action and pathos with a lot of humour. There’s a running joke of the Doctor inappropriately stealing sandwiches. He pinched the Master’s lunch during the second episode, and this time he snaffles Jo’s plate of cheese sarnies from under her nose. Elsewhere, having taken over a RN submarine a Sea Devil is treated with exaggerated (and quite funny) politeness by the crew – although this feels really weird given how a few minutes before they had it at gunpoint.

Next episode: The Sea Devils – Episode Five