This is a treat: the first extant Troughton episode. I was in the audience at the BFI when this was unveiled in 2011, and can still remember the slight deflation (the rumours were The Tenth Planet 4), followed quickly by surprise and delight as the episode unfolded.

That’s entirely due to Troughton’s performance, which is astonishing. The Doctor is ever-watchful, taking everything in, flattering the Professor to get information, playing the fool to save Polly, indulging in some business with test tubes to escape the lab, and calculatingly obsequious to King Thous. He gives a little grimace when he can’t think of a good reason why Ramo should trust him. He delights in dressing up – camply asking, ‘How do I look’ in his splendid Atlantean priest garb, and is disappointed at Ramo’s unresponsiveness. While his problematic characterisation of Zaroff’s mental health issues means the episode probably needs an up-front warning – back in 2011 it got the whole auditorium laughing. Perhaps it’s the distancing effect of telesnaps (or animations), but this is the first time I really feel this is absolutely the old Doctor renewed and delighted to be young again, rather than an impish impostor with a dressing up box.

Nothing in the rest of the episode holds candle to Troughton’s performance. The other regulars wander round some caves looking for something to do. Interestingly, Ben is very much positioned both in dialogue and visually as the lead male companion – Frazer Hines is usually standing behind him, awkwardly leaning into Ben’s conversations with the captured sailors Sean and Jacko, getting into trouble and needing to be rescued – but even so it’s obvious there isn’t enough plot to occupy all three companions, and it must surely have been clear to the production team that at least one of them was going to have to go.

Joseph Furst is magnificently unhinged, but his motivation – to destroy the world – is like Davros’s desire to be set ‘up amongst the gods’ without any of the context that makes the Genesis speech so powerful. That said – a mad scientist making genetic modifications to a captive people from his underground laboratory for nihilistic purposes basically sums up Davros.

Next episode: The Underwater Menace – Episode 3