Even Dogs in the Wild by Ian Rankin (Inspector Rebus #20)

Hands in his pockets, Rebus turned to face Cafferty.
They were old men now, similar builds, similar backgrounds. Sat together in a pub, the casual onlooker might mistake them for pals who’d known one another since school.
But their history told a different story.
Retirement doesn’t suit John Rebus. He wasn’t made for hobbies, holidays or home improvements. Being a cop is in his blood.
So when DI Siobhan Clarke asks for his help on a case, Rebus doesn’t need long to consider his options.
Clarke’s been investigating the death of a senior lawyer whose body was found along with a threatening note. On the other side of Edinburgh, Big Ger Cafferty – Rebus’s long-time nemesis – has received an identical note and a bullet through his window.
Now it’s up to Clarke and Rebus to connect the dots and stop a killer.
Meanwhile, DI Malcolm Fox joins forces with a covert team from Glasgow who are tailing a notorious crime family. There’s something they want, and they’ll stop at nothing to get it.
It’s a game of dog eat dog – in the city, as in the wild.
Even Dogs in the Wild brings back Ian Rankin’s greatest characters in a story exploring the darkest corners of our instincts and desires.