The focus of the episode is the spread of the Silurian plague and the Doctor’s attempts to find a cure. As such, there’s nothing much for the Brigadier and UNIT to shoot at, and for the majority of the episode the Doctor is out of his velvet and into a lab coat testing samples while the Brigadier has lots of urgent phone calls.

There’s a risk that all of that could have resulted in a very tedious bit of padding. Fortunately, the script and direction are really solid on the escalating stakes – Masters’ journey back to London as Patient Zero, and the spread of the plague across the capital (like the Survivors title sequence) make them clear. Combe’s reportage style location work is great: the Marylebone ticket inspector swooning; Masters – looking increasingly dishevelled – journeying back to the Ministry of Science but expiring on the pavement before he can deliver his report; and eventually passengers collapsing, covered in sores.

The cuts between these scenes and the research centre creates the life-or-death tension this needs for 25 minutes, helped by the regulars’ stressed snippiness towards each other: the Brigadier and Liz bark at each other while the Doctor grumbles about the time it’s taking to set up equipment. But equally, there’s no sense that they aren’t a team: elsewhere the Brigadier defends the Doctor and Liz to some over-zealous civil servant on the phone, buying them some breathing space, while Liz rolls her eyes at the Brigadier over Dr Lawrence’s increasingly erratic behaviour.

Peter Miles’ performance has evolved from icy disdain to utter incredulity and paranoia through the last five episodes. Now he really goes for it, portraying Lawrence’s descent into madness with one of the most gloriously OTT performances in the series, screaming:

Well, you can clear out of here, all of you. And take that crazy Doctor with you! And all of your military rubbish! I’m in charge of this place! Well, are you going? Or do I have to throw you out myself!

Before leaping over the desk to attack the Brigadier and promptly expiring. It almost makes up for the weakness of the final cliffhanger: the Doctor gurning as the Silurians wobble at him just like they ended it a fortnight ago.

Next episode: Doctor  Who and the Silurians – Episode 7