Ian Rankin's "Set in Darkness" is actually a reprint of a book he originally wrote and published in the late 1990's. As I have read all - I think, anyway - of his books about Inspector John Rebus, of the Lothian and Borders Police Department in Edinburgh, I was a little worried when I received this book from AmazonUSA that I had read it years before. I was glad to realise I hadn't - it was new to me.
"Set in Darkness" is definitely not Rankin's best Rebus book. It's good enough to enjoy - three plot lines are reduced by the end of the book - but to a novice Rankin-reader, it's a tough slog. John Rebus, a moody, go-it-alone kind of cop, is the bane of his supervisors' existence. Not a team player when it counts in solving a crime or two, Rebus is not a sympathetic character. He is, however, an extremely interesting one to read about. He's surrounded - loosely - by his fellow police officers and works with them, as needed. The "loner cop" is one we've all seen many times before. Rankin does a good job at fleshing out both the good guys and the bad guys in his work, and "Set in Darkness" doesn't disappoint in its nuanced character development. I think, though, the plot sort of fell a little short of great.
If you've never read Ian Rankin, I'd start with one of his other Rebus books. They're all described in Amazon fairly well.