'Mustn't complain' - but people always do.
Nobody likes The Complaints - they're the cops who investigate other cops. Complaints and Conduct Department, to give them their full title, but known colloquially as 'The Dark Side', or simply 'The Complaints'. It's where Malcolm Fox works. He's just had a result, and should be feeling good about himself. But he's a man with problems of his own. He has an increasingly frail father in a care home and a sister who persists in an abusive relationship - something which Malcolm cannot seem to do anything about.
But, in the midst of an aggressive Edinburgh winter, the reluctant Fox is given a new task. There's a cop called Jamie Breck, and he's dirty. The problem is, no one can prove it. But as Fox takes on the job, he learns that there's more to Breck than anyone thinks. This knowledge will prove dangerous, especially when a vicious murder intervenes far too close to home for Fox's liking.