This ends more satisfyingly than Holmes’ previous scripts largely because the plot is so light. A character comedy, this perfectly pays off its three central partnerships. The Graff and Sholakh go out as warriors, albeit in the Graff’s case as a ranting tyrant who engineers his own downfall. Garron and Unstoffe lose the Graff’s money and their jethrik, but land on their feet because Garron always has something else up his sleeve. And the Doctor and Romana seem to have reached a grudging mutual respect as they unveil the first segment of the Key of Time.

The script is full of glorious one-liners, mainly for Iain Cuthbertson: ‘Who wants everything? I’d settle for 90 per cent’; ‘I was going to make a touching speech, but my throat is too dry’. Reunited with the charmingly naïve Unstoffe, who’s the Romana to the worldly Garron, there’s a sense that, had Big Finish felt minded to, these two were every bit as spin-off worthy as Jago and Litefoot. I’d have snapped up a series of Hustle in space in a moment.

Holmes also makes the Graff and Sholakh more entertaining than the straightforward villains they might have been, a very funny double act (Sholakh’s flattery at the Graff’s marksmanship is brilliant, as is the Graff’s line, ‘I flatter myself I know how to get the best from natives’. Paul Seed inserts genuine mania into his performance: his devastation at Sholakh’s death feels real (the tender kisses he plants on his wingman’s face are either deeply homoerotic or a tribute to military brotherhood, or both), and he skirts with going over the top in his final speech while remaining convincingly broken. It helps that as he describes the glorious campaigns of the past, the sound of the battlefield rises.

Against these vivid characters, the Doctor and Romana are slightly, though not disastrously sidelined in a way I don’t expect the script editor Robert Holmes would have accepted from any of his writers. Given it’s her first story, Mary Tamm gets almost nothing useful to do. She looks splendid wandering round the catacombs in her white gown, but that’s about all. The refurbished, less noisy and generally more chipper K9 gets more action. The Doctor does get to disguise himself as a Levithian Invincible, blow up the Graff, and have some comedy business with Garron at the end (Tom is at his most Capaldi-ish as his toothy grin fades and he declares, ‘I do dislike faint praise’) but in general this is about as passive as the fourth Doctor gets. I think that’s one reason why The Ribos Operation tends not to be mentioned in the same breath as The Talons of Weng-Chiang or Pyramids of Mars, even though it’s a beautifully executed story. Knowing what’s to come makes it easier to appreciate Holmes’ last, great comedy masterwork.

Next episode: The Pirate Planet