Do you know what I’m referring to? In one of the Agatha Christie mysteries, Miss Marple mentions a gill of pickled shrimp. I think it went missing from someone’s string bag, and she figured out where it went. For me, the words “gill of pickled shrimp” refer to a mystery that you solve the way Miss Marple solves mysteries, by noticing small details that allow her to reconstruct a sequence of events.

I’m pretty good at that. There are plenty of things I’m not good at, but I’m actually pretty good at inductive reasoning, which is the sort of reasoning that Miss Marple uses, and Auguste Dupin, and Sherlock Holmes. And I’m usually right. I’m also pretty good at understanding people, what they’re thinking at any particular time, what motivates them, what they’re likely to do.

I hope all this allows me to write good detective stories, because I’d like to write detective stories one day. I already have a detective.  And a lovely series of murders all planned out.

I was thinking today about what I had learned from Agatha Christie, and I’ve actually learned a great deal from her about creating characters, not so much from how she creates characters, but from what Hercules Poirot and Miss Marple tell me about characters. For example, here are some things they’ve told me:

1. Everybody lies. That’s true, isn’t it? It’s a sad thing to realize, but if you pay attention to human interactions, and if you want to be a writer, you need to pay attention to human interactions, you’ll realize that everybody lies. All the time. Most often, people lie to themselves. So when you’re writing a character, you need to ask yourself a couple of questions. Who is my character lying to? And why?

2. Everybody is motivated by self-interest. Again, sad if you consider it from the perspective that we’re usually taught to. We’re all supposed to be honest and altruistic, aren’t we? But we’re not. Honest and altruistic characters are interesting to write because they’re so unusual, you almost need to make something wrong with them, like being aliens or something. Otherwise, readers won’t believe in them. They will read as false.

3. Everybody acts within character. What I mean is that people are mostly consistent. They think and act in the ways they’re used to, out of habit. If someone acts out of character, there is usually something going on, something unusual prompting that act. This is not to say that people can’t change, but that they usually need significant motivation to do so, and once they have changed, they settle into a new set of habits. Motivational speakers know this. That’s how they make so much money.

These are probably not very nice things to say about people, but as Miss Marple says, murder is not very nice. In a way, neither is writing. If you want to write realistic characters, you need to make them lie, act out of self-interest, and act within character unless there is a significant motivating force making them act differently.

In other words, you need to know people and represent them realistically.

Sitting here writing this, it occurs to me that knowing people is really the key to writing a murder mystery. It’s not about the clues or the crime, about the mystery you’ve created. It’s about the people involved in that mystery, what motivates them. How they respond.

I have to confess: sometimes I watch 48 Hours Mystery, which is always ridiculously melodramatic, and in which you can always guess whodunnit. (They’re not interviewing the wife, so it’s her. They don’t want to show her in the prison jumpsuit too early in the show.) Just as you can always guess on the CSI shows. (It’s the woman who used to be on that other show, you know, the famous actress.) And that’s what I’m interested in, the motivations. Why do people do the things they do? More than the specifics: how does arsenic actually affect someone? Although even those details are useful and give me ideas for plots.

I hope that someday you’ll get to meet my detective. Her name is Darcy Chase, and her father used to write murder mysteries. But she’s the real thing. And she’s very good at inductive reasoning. She could tell you who took the gill of pickled shrimp, just like Miss Marple.