All I wanted to know for much of this book was who that poor young woman was, the girl who suffered such a fate and who did it. That you are reminded of this first, terrible act throughout the book only makes the reader more keen to finish this riveting read and solve the mystery with McLean.
The tone is not all horrifying gore. The characters bring a well needed injection of humour and mystery and a sense of realness. The reader is slowly fed information about McLean, his past does not overshadow the story at all.
This is a well rounded crime novel, with just enough of everything to make it perfect. James Oswald surely knew that to write about a Detective Inspector in Edinburgh would invite comparisons to Ian Rankin's Rebus and seemingly makes a nod to this near the very end, with a Police Constable reading one of Rankin's books.
I wasn't sure about the slight fantasy element at first, but it worked well with the story and resolved itself by the end. It's written in such a way that it's up to the reader to decide whether they want to include the fantastical or not. I've never read such a real crime story so well-woven with a hint of fantasy, and I thoroughly enjoyed it.