I think the one of the main problems with this book is that it doesn't really know what it wants to be. It can't seem to decide whether it's "chicklit" (vile term) or a hardboiled detective novel and as a result it doesn't really manage to be either of them at all convincingly.
Another problem I had with it was that I found it hard to muster up much empathy for the main character. I usually rather like rebellious protagonists who defy authority, but usually they're doing it for a reason - Izzy Spellman seems to do it for the sake of doing it and I find that unsympathetic. Towards the end of the book I found I had more sympathy for Izzy than for any of the other characters, but that really wasn't saying much.
It doesn't help that the story is told in a disjointed series of flashbacks, especially since another book I'm currently reading (Beloved by Toni Morrison) uses a similar technique much more effectively.
On to the plot, such as it is. Izzy Spellman is literally born into detective work and inherits her parents' natural aptitude for it. But she also has a rebellious streak a mile wide and her whole family are borderline insane - following each other, tapping phones and generally giving each other no privacy. Izzy finally snaps and wants out. Her parents insist she should work one last case. She agrees.
It's hard to say much more than that without spoiling the rest of the story, thin though it is. I think the Spellman shenanigans are supposed to be funny, but they struck me as pathetic (in the original sense). These are tragic people, incapable of living normal lives.
There is, apparently, a sequel in the works. I don't think I'll bother.