One of my former students, who is an intelligent and voracious reader, asked me this question when I announced on Facebook that I'd like to hear questions about writing.
I have a couple of theories. My first would be that we love to figure out and solve problems. Often I read and read to get to the end of a mystery because I haven't figured it out and I'm dying to know how it ends. An effective writer can hide those clues so they are in plain sight, but we don't catch them because of the writer's craft. Actually it is important that the writer leave clues in plain sight because readers become very unhappy when the clues are left until the last ten pages of the book. It doesn't give them a fair chance.
I just finished an amazing book by Thomas H. Cook called The Chatham School Affair. His writing style is gorgeous and lyrical. His story is told first person by an elderly lawyer who, earlier in life, was the son of the school's head master and a student at the school. The tale is dark. It is about a terrible event at this private school, an event beyond imagining.
But Cook is clever in giving the reader pieces of the jigsaw puzzle here and there. He flawlessly combines past, present, and future in his narrative and he does it so seamlessly that the reader is constantly left guessing the details of this terrible event. Suspense is everywhere--the reader knows something terrible happened from the first pages, but she doesn't know what it was. Only when the reader comes to the end does she see how it all fits together. It is a perfect example of why we can't put mysteries down.
I believe a second reason we love mysteries is because they show us a darker side of human nature, a side that many believe we all have but keep in check--unless, perhaps, we are serial killers or sociopaths. The idea of a "good person" coming in contact with someone who has unleashed that darker side is an intriguing combination.
I was reading another blog today--"At First Glance" by Sandra Parshall at the blog, Poe's Deadly Daughters. It referred to a recent article in Psychology Today called "What's In a Face?" that discusses whether our first impressions of people are accurate. Can we spot criminals when we first see them? I believe our curiosity about these people and situations is one of the reasons we read mysteries. We could have brushed past a killer on the street and not have known it. But we can read about these killers in mysteries and we can do so in the safety of our arm chairs. Whew! That's a relief.