It is everything that a good mystery should be, in my opinion. A plot that keeps you thinking and guessing all the way through, characters that are realistic in their thoughts and actions, and a satisfying resolution at the end.
I really enjoyed the storytelling technique in this book. The action takes place over only 2 days, and the narration, while always in the third person, jumps around from character to character. Which means that in one chapter you are present with Lucy in the middle of the interrogation of a suspect and observe her to be pulling some maps up on her computer, not quite sure how they relate to the plot; and then in the next chapter you have Kay receiving the maps on e-mail and yes, they are very relevant.
This was a 1-week loan from the library (as are all books with a waiting list), and I finished it well before it was due back. This is a good thing, since it is a book that definitely benefits from reading over a short period of time in order to keep track of all of the plot lines. At times, I would get confused (ie "Hunh?! What is he talking about?"), only to have the missing details supplied later on as the story is gradually revealed.
One proviso - the plot does hinge on events that happened in previous books, so if you haven't been following the series, this book may not be the best entry point.
So a good read, and an entertaining way to spend the weekend. I'm looking forward to her next book - hopefully I don't have to wait too long!