Five Rules I Stole From Christie
(And One I Broke on Purpose)
It started, as these things always do, with a reread.
I was sitting in the writing nook by the window last Tuesday evening, rain doing its very best against the window, Carruthers presumably stalking something outside, and I had picked up a dog-eared copy of The Body in the Library. Just for a few pages, I told myself. Just to get back into the groove.
Three hours later, the tea was stone cold, the plot of my own book had rearranged itself in my head, and I had filled half a notebook with scrawled observations about why Christie is simply, infuriatingly, still the best.
She left us clues, you know. Not just in her books, but in how she built them. After years of reading her, and now writing my own Harmony Stone mysteries, I’ve come to think of her craft as a kind of invisible checklist. A set of rules so elegant you barely notice them working.
I follow five of them faithfully. The sixth one? Well. We’ll get to that.
Rule One: The Village as a Closed World
Christie understood something that takes some writers years to grasp: the smaller the world, the bigger the stakes.
St Mary Mead isn’t just a backdrop, it’s a trap. Everyone knows everyone. Everyone has a past, a grudge, a secret they think is buried safely in the churchyard of local memory. The village doesn’t let you escape. It just lets you pretend you have.
When I built Kingscombe, I knew it had to work the same way. It had to feel like a place where nothing stays hidden for long, and yet, somehow, everything does.
The Cream First Café is where the gossip flows as freely as the cream tea. The harbour is where people watch each other sideways. And Mossington Manor looms over it all like a question nobody quite wants to answer.
Harmony arrived in Kingscombe thinking she was stepping away from complexity. She was mistaken. This small town had other plans.
Rule Two: The Amateur Sleuth Who Is Underestimated
This is Christie’s most subversive trick, and I adore her for it.
Miss Marple is an elderly woman who knits and keeps quiet at dinner parties. Nobody sees her coming. That’s entirely the point. She moves through a world that has already decided she is harmless, and she uses every inch of that invisibility.
Harmony Stone is a retired schoolteacher. She turns up in Kingscombe to cat-sit in peace with a pile of books, a pair of running shoes, and an interest in local history. The local police think she’s invisible. The suspects think she’s nosy, but harmlessly so. The reader, of course, knows better.
There is something deeply satisfying about a woman of a certain age who notices everything, says very little, and is consistently underestimated. Christie built a whole career on it. I’m borrowing the blueprint with enormous gratitude.
Rule Three: Red Herrings Must Play Fair
Here is the rule that separates the good from the great: a red herring must be genuinely plausible. It must deserve suspicion. It must feel, right up until the moment it doesn’t, like the real answer.
Christie never cheats. Every clue she plants is there. Every misdirection is earned. You could, theoretically, work it out — but she is simply cleverer than you, and she knows exactly when to dangle the wrong thread.
In The Mystery of Mossington Manor, I spent a considerable amount of time making sure the real culprit was hiding in plain sight, and that the wrong suspects were each wrong for entirely convincing reasons. Whether I succeeded, I’ll leave to you to judge. But I can tell you this: I rewrote the entire Kingscombe May Day scene four times to make sure the clue was there without being obvious. Four times.
Christie, I suspect, got it right on the first draft. But then she was a genius. That’s why she’s my mentor.
Rule Four: The Death Must Matter
In cozy mysteries, there is sometimes a temptation to treat death as a plot device, a convenient inciting incident, neatly removed from grief.
Christie never quite does this. Even when the victim is unlikeable (and she does love an unlikeable victim and so do I!), there is weight to their absence. The world has been disturbed. Something real has ended.
I think about this with every book. The victim in Mossington Manor is not a simple person. They are not meant to be. Harmony’s investigation uncovers a life that was complicated, contradictory, and, in some ways, rather sad. The mystery wouldn’t work if it didn’t. The solution only lands if you’ve been made to care, even a little, about who was lost.
Cozy doesn’t mean weightless. It just means the weight is carried gently.
Rule Five: The Reveal Must Gather Everyone Together
The drawing room scene. That glorious, theatrical moment when Poirot (or Marple, or any Christie detective worth their salt) assembles the suspects, delivers a masterclass in observation, and, with immaculate timing, names the killer.
It works because it mirrors how we all secretly want justice to work: publicly, clearly, with everyone in the room, nobody able to escape.
Harmony does gather everyone. She always does. She needs to because she works things out by watching faces, not just evidence. But I should warn you: she doesn’t do it in a drawing room.
I’ll say no more.
The Rule I Broke: The Establishment Always Helps
In Christie’s world, the police are a fixed point. Sometimes bumbling, sometimes competent, always ultimately present. Poirot has his contacts. Marple has her nephew. There is a structure, and even when our sleuth circumvents it, the structure is there to be circumvented.
Harmony has PC Shaun Weathers. A wannabe detective studying for his promotion at night.
Shaun is good at his job and has ambition. He is also, understandably, not terribly delighted about a recently arrived retired schoolteacher wandering through his crime scene with a cat and a lot of well-intentioned questions.
The relationship between them is tense, and at best, a grudging détente that serves both their interests, and at worst, a polite war of attrition conducted entirely through meaningful silences and very pointed cups of tea.
Christie’s sleuths eventually win the establishment’s respect. Harmony is working on it. She has made some progress. But I wanted to write something that felt honest about what it looks like when an intelligent woman turns up where she wasn’t invited, and isn’t welcomed, immediately, with open arms.
It felt more true. And sometimes, truth is more interesting than tidy.
Your Turn, Fellow Sleuths
Christie’s rules aren’t constraints — they’re a gift. A framework built by someone who understood, better than almost anyone, that a mystery is a promise to the reader.
Play fair, lay out the clues in plain sight, and keep the faith because order will be clutched from the jaws of chaos.
I try to. I don’t always succeed, but I’ll always be grateful to Agatha for her books and her guidance to mystery writers.