A school shooting...but really, more of a shooting that happened to take place at a school. It's straight-forward, the where what and who and how laid out for the police to read easily, and if all that wasn't enough, an eye-witness that tells it just like it seems. But it wouldn't be a book if it were that easy.
I really love Laura Lippman. All of the books I've read that she's written have a fantastic moodiness to them, an urgency even when the crime is done and no one's in danger anymore. They have great characters, who are imperfect and believable, flawed but sympathetic--you might love or hate any of them, and you'd be right to do so. And they all have a great sense of place--the setting is a second protagonist, as complicated and important as any of the characters.
I just think she's a great writer, and really, there's no other mystery writer I'd rather read. I really really liked this book.