‘The Master must have precipitated an eruption.’ You can tell this is a post-Return of the Jedi story because suddenly everything’s about fathers and brothers. Turlough’s discovery of his own brother means that we’ve met family for every JNT companion (and he introduced Sarah Jane’s auntie, too) compared to none bar Leela’s dad for pretty much any previous era. At the end of this it’ll be a surprise if the Master doesn’t turn out to be the Doctor’s secret brother.

This continues to be pleasant without exactly setting the pulse racing. The Doctor is slightly less diffident this time, as he imposes his will on Kamelion (‘Servile, slave’ – bit mean), confronts Turlough for keeping things from him, and deduces the Master’s plan from a lick of numismaton gas residue. I like Turlough’s quick thinking – a hallmark of the character seen particularly this season – to switch off the crematorium gas supply, describe the Doctor as ‘an elder from the City of Gallifrey’ and to herd the vulnerable Sarnies (as they’re presumably known) inside the TARDIS to escape the Master’s volcanic fiddling. But a lot of it still consists of the Doctor standing about away from the main action in a broken-down TARDIS.

Ainley and Wyngarde, though, are compulsively watchable here. Wyngarde’s quiet dignity and soft-spoken dialgue gives Timanov a genuinely priestly presence. Ainley goes the other way, making the Master hiss like a cat when he ignites the numismaton gas, striding around his rather nifty-looking control room and the volcano power room spitting out insults (‘that galactic philanthropist‘, ‘stop mewling’). Peri’s almost been his companion for this story, so when it comes to finding out what’s in the box it’s fitting that she should be the one to discover – it’s the Master, reduced in size but not in malevolence. For once, it’s a very funny cliffhanger.

Next episode: Planet of Fire – Part Four