1. The mystery itself.
2. The characters, how they develop, and the world they live in.
Every mystery starts off with a question. How did the body get in the locked room and who killed her? Or, in the case of the latest book I read, Peter Blauner's Slipping Into Darkness, how did the blood of a victim buried 20 years ago end up under the fingernails of another dead girl - right after the man convicted of the first girl's murder has been released from prison? That's the hook, the thing that gets you to start reading the book in the first place.
Next, the detective (amateur or professional) begins to try to solve the mystery. In Slipping Into Darkness, homicide detective Francis Loughlin tries to figure out what happened. Had they misidentified the first girl's body, 20 years earlier? Had there been a mix-up in the DNA testing done only now? Is it possible she is still alive? That she has a long-lost sister? What links the two women - or is it only coincidence?
And, in the more intersting development, we learn that Francis is going blind. His symptoms may become obvious very soon, soon enough that he won't get the bump in the pay grade he is only a few months from, and forcing him to retire on even less. We also meet Julian, the Puerto Rician super's son Francis was so sure did the murder.
So the book raises new questions. Did Francis fudge the facts when he helped put Julian away? Will Julian be able to cope with a new world? When Julian first goes into a Starbucks he is enchanted. He plans to come back again and again to his new favorite restaurant. He is nonplussed to discover it's a chain with an outlet on every block. E
veryone he meets treats Julian with suspicion. He got out on a techicality. Even his own lawyer sometimes flinches away from him. And prison has taught him to be a violent man. The reader does not know whether Julian did the crime or not, nor what exactly Francis did to make sure that Julian went to prison.
The book is a pleasure to read, full of wonderful description that fits each character perfectly. It's a very visual book - I could see all the characters in my head as each made an appearance. When I had a spare 10 minutes, I wanted to be reading. It's a rare book the enchants me so much.
The end, though, feels rushed. Answers to such intriguing questions are never easy. In this case it feels like the author has put together a jigsaw puzzle and had to hammer down the last few pieces to get them to fit. He shows it to you and then snatches it away before you notice that some of the pieces are already starting to pop apart.
But does this diminish the pleasure of the book? Only slightly. The rest is perfect. All mytery authors are faced with the problem that it is much easier to raise an intriguing, impossible question than it is to answer it. Only a few books, like Persumed Innocent, manage to raise the question and provide an answer that makes the reader gasp and nod knowingly at the same time.
I'm probably as guilty of this as anyone.