Mystery Writing 101: Play by the Rules—or Don’t

The best mysteries keep readers guessing—and sometimes, breaking the rules is the best way to do it.

📝 448 words. ⏳ Estimated reading time: around 2 minutes.

Writing a mystery isn’t just about who did it. It’s about how you let your readers figure it out. Nobody likes a mystery where everything is solved out of nowhere. We want to play detective too! That’s where the idea of a “fair play” mystery comes in—stories where the reader gets all the clues they need to solve the case.

AI Image by leonardo.ai / Prompt & design by the author.

Back in the 1920s, two guys—Ronald Knox and S.S. Van Dine—came up with rules for writing mysteries.

Knox had his “Ten Commandments,” like, “Only one secret passage allowed,” and “No wild science experiments, please!”

Van Dine gave us 20 rules, making sure the detective doesn’t win just by luck. (No “Oops, I found the culprit!” moments!)

But here’s the thing—rules can be bent. Or twisted. Or completely broken. Even these two rule-makers contradicted themselves sometimes. For example, Van Dine said, “No romance in a mystery!” But seriously, who doesn’t love a little drama?

Break the Rules, Make Your Own

Don’t think these rules are set in stone. Sure, they’re helpful, but sometimes the best stories come from bending them a bit. Take Agatha Christie—she made her detective the criminal in one of her books!¹ Knox probably wasn’t thrilled about that.

So, what should you do? Here are some simple, no-fluff rules to get started:

1. Give clues, but don’t make it too easy.

   Readers need to feel like they can solve the case. Drop hints, but don’t spell it out.

2. Make it make sense.

   The solution should reward smart readers. They need to connect the dots with logic, not luck.

3. No fancy stuff that nobody understands.

   If you make up a poison or gadget, explain it clearly. Don’t make readers search online to figure out how it works.

4. No lucky guesses.

   The detective needs to solve the crime using their brain—not by tripping over the answer by accident.

5. Don’t trick your readers.

   The detective can’t lie to us! Maybe they don’t share everything, but no outright deception.

6. The murderer has to matter.

   They shouldn’t be some random person in the background. We need to know them, even if we don’t think they’re guilty.

7. Murders should be on purpose.

   The killer has to plan it. No “Oops, I killed someone” moments.

Have Fun with It

Mysteries are fun because they have rules and let you break them! You get to decide how much you follow or bend. So go ahead, challenge yourself, and make your mystery exciting!

Good luck, detectives! Keep your magnifying glasses ready, and remember: the answer is out there—you just need to find it.

What rules do you like to break? Let me know in the comments!

—Simon

Hey there! I’m Simon, a business owner who’s totally passionate about writing (and one day, I hope to marry the two!).

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Here’s the latest on taking your reading seriously. In this insightful piece (pun intended),

Sarah Orman

shares tips that helped her transition from reader to writer.

I recommend checking it out if you’re looking to enhance your own reading practice.

5 Ways to Read like a Writer

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1. If you’re part of the 1% of crime fiction readers who don’t know, I’m referring to The Murder of Roger Ackroyd published in 1926. In it, Agatha Christie made a bold, rule-breaking move that is still admired for its cleverness today.