Think about Agatha Christie’s, Miss Marple. Why do we like her as a character? Why does she entertain us?
First of all, she’s old. That immediately sets her apart from most other fictional detectives and makes her different. She’s also a lay person and a bit of a busybody, who just happens to find herself in a number of sticky situations. What else do we know about her? She’s never married, is always knitting something, and is good at puzzles, i.e. putting two and two together. Because we think of her as the kindly grandmother type, she easily fades into the background (along with her knitting needles) - a good place to be if you want to listen and learn.
Jane Marple’s very presence puts people off guard, and other characters often say more than they mean, or are overheard to give themselves away. But an important part of Marple’s character is what she does with the information she gleans. She is a shrewd old bitty and has an uncanny ability to identify “markers” that inevitably lead to solving the crime. I say markers, and not clues, because Marple is very good at reading human nature and understanding the prevailing culture at the time, and how those things may contribute to the mystery. But she’s also good at uncovering clues and weaving them together to complete the narrative. And even though there is almost always a police constable or detective on the scene, we believe (as readers) that these murders just might never get solved without the help of Miss Marple.
The best mysteries however, also have compelling villains. Why is that important? Because the villain’s personality provides the motivation for the murder in the first place, and sets up the adversarial relationship with the detective. Let’s take Norman Bates, in Psycho. We get to know him as a rather shy, awkward character in the beginning, who clearly is interested in the young woman who checks into the motel. As the story evolves however, we suspect there is more to this character and his relationship with his mother. Once we know that he is not only the killer, but the “reincarnated” personification of his mother, we love (to hate) the complexity of his character. He’s been dominated by an overbearing mother, killed her (along with her lover), and then transferred her personality with his to commit other murders. Wonderful!
When mystery writers gloss over characterization in favor of plot, it is at their own peril. These are the books I tend to put down. Readers want to be engaged, and what’s more engaging than a compelling character working within the structure of a complex and intriguing plot?