My ancestry is Scottish. I was born in New Zealand, but my family line (on both sides) is only a couple of steps out from Scottish soil. So, it wasn't random that I set a large chunk of my latest short story, Alan Duncan Did This, in Edinburgh (Alfred Hitchcock's Mystery Magazine, March/April 2026). My story is about a Scotsman, Alan Duncan, who travels down to London on Guy Fawkes night (1949) to commit a murder. A murder he's quite proud of. A murder he ranks as a work of art.
Fletcher's murder had been a work of magnificence. Alan almost wished he could have signed it. With a bold, florid flourish, like Salvador Dali. Alan Duncan did this.
Vanity? Yep. A villain's vanity was a common theme in Agatha Christie's mysteries; it was often her villain's downfall. Anyway, in this post, I don't want to chat about Scotland or a murderer's vanity, but about motive. Alan Duncan had a good, cogent reason to commit his murder. Killers in fiction should.
Detectives are always looking for means, motive, and opportunity. But in real life, motive is the lessor of these in criminal investigations. It's not required for establishing guilt or gaining a conviction. It's nice for the prosecutor to have one in their basket going into a courtroom, but it's unnecessary to prove. For writers of mysteries, however, motive is the central key to a character's actions. It's the engine on which a story is propelled.
People don't commit murders for weak reasons in fiction. Without a strong, compelling motive, a character's actions reek of implausibility. Yes, in the real world, killers can and do commit murders for no reason, but that doesn't really fly in fiction (there are exceptions, so I'm speaking in general). Spoiler: Imagine if the killers in Murder on the Orient Express had meticulously plotted and killed Ratchett/Cassetti because he stole Princess Dragomiroff's polo mallet. Weak sauce.
Strong and clear motives engage the reader. And audience. Shakespeare was a master of this.
- Macbeth (back to Scotland) murders King Duncan through ambition; he wants the crown, and to allay the doubts of his wife and demonstrate his power. His motives are ambition and ego.
- Richard (Richard III) needs nought from a wife to spur him to action; his ambition has no hesitation when he orders the murder of, or personally dispatches, a succession of nobility to the hereafter. His motivation is also revenge against the world. He is a man bitter with resentment.
- Iago (Othello) is also motivated by resentment (Othello's promoting of Cassio rather than himself), and sex (the suspicion that Othello has slept with his wife). “I do suspect the lusty Moor hath leaped into my seat.” Envy is Iago's principal motivation. He envies everything about Othello. And it's true that Iago doesn't actually murder Othello, but he does systematically destroy Othello and lead him to kill his own wife. Revenge writ large.
These are all strong motivators because they are plausible in their contexts and thoroughly human. We might not condone a character's actions, but we instinctively understand their reasoning.
It's often remarked that sex or money are the most common motives for murder in crime fiction. Cherchez la femme. Cherchez la dollar. Here's my stab (see what I did there?) at a start of a murder motive taxonomy based on these two headings:
| SEX | MONEY |
|---|---|
|
|
To sex and money, as per Shakespeare above, I would add revenge.
Revenge is often egged on by sex or money. Alan Duncan's motive is revenge by way of sex – jealousy and obsession. He focuses his whole life on seeking revenge because of his jealousy. Murder is his only release from his idée fixe.
Revenge can also stand alone. Spoilers: Murder on the Orient Express is a murder of plain and simple revenge. The actions of the killers are not invoked because of sex or money (however, what they are avenging was a crime involving money (a ransom)).
This is only the tip of the iceberg of murder motives. Do you have a favourite when you write, maybe one that isn't in this list?















