Burke is best known for his 2006 stage play Black Watch about Scottish squaddies in Iraq; Rankin approached him to write the series because he knew Burke would be good at capturing the vulnerability that Rebus’s toughness exists in part to mask. (His military past has left him with PTSD, which affects him particularly badly whenever he fails to prevent a murder.)

“Greg’s always been fascinated in his work in the macho exterior of the Scottish male,” says Rankin, “but also the frailties and the fears that lurk just below that façade.”

This volatile characterisation of Rebus reflects a recurring theme in the most recent novels: the re-examination of Rebus’s past behaviour in an era less inclined to tolerate police rule-breaking. He has been investigated for evidence-tampering, cover-ups and worse: there have been hints that the next book, Midnight and Blue (published in October), will see him banged up for murder.

The pervasive corruption of the police in general has also been a dominant motif. “I think anyone who writes police procedurals in contemporary times has to be aware that police are not regarded universally as the heroes any more, so you have to represent them warts and all,” says Rankin.

“The last couple of Rebus novels have borrowed things that have happened mostly within the Metropolitan Police but extending that to Scotland, saying there’s no reason why that can’t happen here: the police covering up grievous and serious errors of judgment and crimes.

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“Younger writers are steering away from writing about cops. They’ll write about amateur detectives, they’ll write psychological thrillers that don’t need the presence of a police officer, because it’s getting tougher to present a police officer in heroic terms.”

Things may be changing, however. “One of the things we wanted to explore was how Rebus’s attitudes might be very different from some of the younger officers,” comments Burke. “He was one of those policemen who grew up in the Lothian and Borders police [disbanded in 2013], which had a very fearsome reputation: they ruled Edinburgh.”

Younger police officers no longer think they should be a law unto themselves, which brings its own problems, says Burke: “What many policemen will tell you now is that the villains used to be scared of them and they’re not anymore. Although that is to do with budget cuts as well as attitudes changing.”

The new series sees Rebus clash with his progressive young DC Siobhan Clarke (Lucie Shorthouse), who, to make matters worse, is English. “It reflects that Edinburgh is a contested city, where lots of Scottish people don’t live anymore: it’s too expensive,” says Burke. “The toon’s a theme park these days,” Rebus rages at Clarke. “F---ing Instagrammers. Quidditch nonces.”

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Clarke is one of several characters whom Burke has taken from Rankin’s books: others include the gangster Darryl Christie and the police complaints investigator Malcolm Fox (“A very Edinburgh character but of a different kind, a stickler for the rules, almost a fundamentalist presbyterian type,” says Burke).

Rankin “gave me carte blanche”, Burke tells me, when it came to how he used the source material, so he has come up with an original story with characters, plotlines and ideas plucked from various stages of the Rebus canon. “The word ‘Rebus’ means puzzle, and I’ve made it a [jigsaw] puzzle in a way, a mosaic of things that the readers will recognise.”

Part of the intensity of the new series is due to its placing Rebus’s disastrous family relationships, largely ignored in the ITV version, centre stage. Rankin is particularly pleased that Burke has made Rebus’s brother Michael a central character in the story.

“I threw him away kind of cheaply very early, and later I wished I’d kept him around. And Gregory latched on to him straight away and said there’s a lot we can do with the relationship between these two.” The first episode reveals Rebus to be, surprise surprise, not the best sibling or parent: he punches Michael across the room for backchatting him, in the presence of his 12-year-old daughter (“Mum’s right: you are an arsehole”).

What truly fascinates Burke are the dualities in the Rebus stories, the pairings that are different sides of the same coin: Rebus vs Michael, Rebus vs Cafferty, and, above all, Rebus vs himself. “[Rankin] writes in a continuum of the literature of east Scotland, of the dualism of [Robert Louis] Stevenson’s Jekyll and Hyde and James Hogg’s Justified Sinner.”

Rankin agrees. “I’ve just been to Samoa to pay my respects to Robert Louis Stevenson’s grave – which I won’t do again because it’s a hell of a climb – because he set me on this path, as it were. There’s always a conflict going on within Rebus, those two sides of him, the Jekyll and Hyde, at war. There is a good guy in there. And that’s why, despite everything, we end up rooting for him.”

Rebus is on SBS On Demand.

The Telegraph UK