Obviously there is a gimmick to this book. Fiona has something psychologically off kilter, and we don't learn what it is for quite a while. Harry Bingham does a great job building up the tension until the big reveal.
Fiona, "Fi," is a more accessible Welsh version of the tough women heroes created by Carol O'Connell (Kathy Mallory) and Stieg Larsson (Lisbeth Salander). Fi is smart (philosophy degree from Cambridge), meticulous ("I like things orderly. I's dotted, T's crossed."), and has some hidden yee-haw attributes, which are revealed periodically.
Fi's bosses don't know what to make of her. Other detectives are obviously wary of partnering with her. She tries really hard to follow the rules. And sometimes doesn't succeed. It's just that when an idea strikes, she's carried away with it. It's not that she doesn't know she's going off base, because she concocts schemes to hide what she's doing. Since she is the narrator of the story, we get to hear the wobbly wheels turning in her head. And it's a treat.
After Fi manages to insert a toe in the doorway of a big case, the rest of her uncaged personality soon follows. A prostitute and her young daughter are found murdered. It would be a more mundane case, except a bank card bearing the name of a local magnate is found with the body. Too bad that man is also dead. Like a dental tool probing a cavity, Fi chips away to find the decay within the community.
Bingham achieves a great balance between character and plot. It's easy to be intrigued by Fiona's mysterious past and admire how she comes up with insights into the case. Bingham also has a great feel for describing her moments of revelation or emotional catharsis, and it's hard not to give a silent "whoo-hoo" or "aww" in support.
I want this to be a series. I want the next book in the series. I want it now.