Frank Winter is a grumpy cynical ex-sheriff who has been working as a cleaner for the last fifteen years. He likes his drink and he “looks like Johnny Cash on a three-day drunk”. Detective Nunzio Arabito is a twenty-nine-year-old strategic analyst for the Boston Police Department, moonlighting one night a week as an Italian chef. He is responsible for the Prevention First programme and is idealistic about minimising crime and preventing recidivism.

Frank and Nunzio come into each other’s lives when, after twenty years, Barry Krupke is paroled from prison. Krupke has been serving time for the murder of one woman and the abduction of another; he was found not guilty of the murder of a third woman. Nunzio is keeping an eye on Krupke, making sure he stays out of trouble. He is also keeping an eye on Frank, because one of the likely sources of trouble for Krupke is Frank, the third woman being his daughter, Evie. When the verdict was passed, Frank was filmed on national TV, in his police uniform, waving a firearm and saying he’d gun down Krupke if he ever got out of prison.

Needless to say, that incident put Frank on the road to becoming a humble cleaner – although he says the booze was sending him that way anyway. But when he hears Krupke is out, and when he loses his cleaning job over an altercation about his suddenly non-existent pension fund, Frank has free time to consider whether to act on his historic threat or not. And Nunzio is savvy enough to guess where those considerations might lead.

Frank is racist – would never buy a Japanese car because of the war, assumes a black man would steal a camera. He is sexist, grumping that women wouldn’t do as they were told, using language such as “titty bar” and “two-bit street whore”. He is homophobic, feeling uncomfortable around gay men. But he loves his dog to bits, is relaxed with a transexual woman, and as we learn his back story, his behaviour towards his estranged wife Mary is tender and moving.

Frank becomes quite protective of Nunzio: “He should be a social worker – he certainly wasn’t cut out to be a cop.” Nunzio is a delightful character. He is humble, putting up with the banter coming his way at the station, and with being treated like a dogsbody. But he is persistent and very smart. He is also self-deprecating, recognising that he was being brave at one point because “the fear of being ridiculed overcame his fear of sudden death.” Despite his bravado he knows he looks “about as intimidating as Tintin”.

Krupke studied while in prison, stopped drinking, took a course on empathy, and worked out to peak fitness. He also started an online business: “Just like Amway, but with guns”, and is making good money. He’s clean, sober, and knows he can’t be tried again for the events of twenty years ago. But then he discovers Frank is still holding a grudge – and things start going seriously awry. Krupke has one thing in common with Frank – both “always had a tendency to rush in a little heavy handed”.

The plotting of Double jeopardy is great, leading up to a thrilling denouement, that makes Frank have second thoughts about at least some of his prejudices, and about his fitness. All three main protagonists develop through the book, some courage seeping from Frank to Nunzio, and optimism flowing the other way. Krupke realising the difference between the performative radicalism of his United Militias of America, and the messy reality of the field. And there are great secondary characters, and indications that some of them will return if Frank and Nunzio ever get together again, which would be a very good thing.