Midnight and Blue (Inspector Rebus, Bk. 25)

John Rebus spent his life as a cop putting Edinburgh's most deadly criminals behind bars. Now having been convicted of a homicide, he's joined them…
 
A convict is brutally murdered in his locked cell deep in the heart of Scotland’s most infamous prison. Sleeping in a cell across the floor lies John Rebus, the equally notorious detective. Stripped of his badge and estranged from his police family, he is now fighting for his own life - protected by an old nemesis but always one wrong move away from the shank. As new allies and old enemies circle, and the days and nights bleed into each other, even this legendary figure struggles to keep his head.
 
They say old habits die hard, though. The death stirs Rebus’s deductive - and manipulative - impulses, setting off a domino-chain of scheming criminals, corrupt prison guards and perhaps only one or two good souls who may see it all through.
 
But how do you find a killer in a place full of them?