Detective School · Part 1 of 8. A friendly, plain-English guide to murder-mystery logic puzzles for brand-new sleuths. A new lesson arrives every Friday.
Murder-mystery puzzle books are everywhere this year. They’re on bestseller lists, in gift guides and, very possibly, on your bedside table, looking at you with a slightly smug expression.
If you’ve just bought your first one and you’re not quite sure where to start, you’re in exactly the right place. Welcome to Detective School. No exams, no uniforms, and the only thing we’ll be killing is time.
By the end of this first lesson you’ll know what a murder-mystery logic puzzle is, how it differs from a mystery novel, and you’ll have solved a small case of your own.
So what is a murder-mystery logic puzzle?
It’s a whodunit where you are the detective. Instead of reading a story and waiting for the clever inspector to explain everything in the last chapter, you’re handed the evidence and asked to work it out yourself.
The evidence usually comes in two parts:
- The case file: who was there, and the facts about them. Where they were, what they carried, when they arrived.
- The clues: short statements about the culprit, like “The killer was not in the Dining Room.”
Put the two together carefully and only one person can possibly be guilty. That’s the promise.
How is it different from a mystery novel?
A good mystery novel is allowed to keep secrets. It can hide a twin in the attic, reveal a forged will on page 300, or let the detective notice something the reader never saw.
A logic puzzle plays fair. Puzzle-makers call this fair play, and it means three simple things:
- Everything you need is on the page. No secret twins. No surprise confessions.
- There is exactly one answer. Not “probably the butler”. One name, proven.
- You never need to guess. Every step follows from the clues, the way one domino knocks over the next.
In a novel, you’re a passenger. In a logic puzzle, you’re driving. (Mind the hairpin bends.)
The two styles you’ll meet
Most murder-mystery puzzle books use one of two styles, and some mix them:
- Grid puzzles. A small cast, say four suspects, four rooms and four weapons, and you match them all up using a grid of ticks and crosses. If you’ve tried my beginner’s guide to logic puzzles, you’ve already met this style.
- Elimination puzzles. A list of suspects, sometimes a very long one, and a set of clues. Each clue rules people out, and you keep going until only one name is left standing. My casebooks work this way, just on a much grander scale.
Today we’ll try a small elimination case, because it teaches the single most important detective habit: rule people out, one clue at a time.
Practice case: The Lighthouse Supper
(The picture at the top is mood, not evidence. Everything you need is in the text below.)
A storm has trapped eight supper guests inside the old lighthouse on Gull Point. At a quarter past eight, the keeper, Captain Ossian Gale, takes one sip of his cocoa and keels over, poisoned. Someone at supper is responsible.
The lighthouse keeps a guest book. Here’s what it says (“Time” is when each guest arrived):
| No. | Guest | Room | Carrying | Time |
|---|---|---|---|---|
| 1 | Ada Finch | Library | Umbrella | 7:05 |
| 2 | Basil Crane | Conservatory | Pipe | 7:40 |
| 3 | Cora Moss | Library | Gloves | 7:55 |
| 4 | Dorian Pike | Dining Room | Pocket watch | 7:20 |
| 5 | Edith Rowe | Conservatory | Gloves | 8:10 |
| 6 | Felix Hart | Dining Room | Gloves | 7:50 |
| 7 | Greta Lowe | Library | Pocket watch | 8:05 |
| 8 | Hugo Penn | Conservatory | Gloves | 7:30 |
And here are your clues. Take them one at a time, in order:
- The killer arrived after 7:30.
- The killer was not in the Dining Room.
- The killer was carrying gloves.
- The killer arrived before 8:00.
How to work it: grab a pencil. For each clue, go down the list and cross out every guest who doesn’t fit. Write down how many guests are left after each clue. Detectives call this a ledger, and it’s your best friend when things get long.
Who poisoned the Captain’s cocoa? Decide before you open the envelope.
· · ·
Open the sealed envelope: the solution
The killer is No. 3, Cora Moss. Here’s the ledger:
- “Arrived after 7:30.” Cross out Ada (7:05), Dorian (7:20) and Hugo (exactly 7:30 isn’t after 7:30). 5 left: Basil, Cora, Edith, Felix, Greta.
- “Not in the Dining Room.” Cross out Felix. 4 left: Basil, Cora, Edith, Greta.
- “Carrying gloves.” Cross out Basil (pipe) and Greta (pocket watch). 2 left: Cora and Edith.
- “Arrived before 8:00.” Cross out Edith (8:10). 1 left: Cora Moss.
Notice two fair-play touches. Every clue removed at least one guest, so no clue was wasted. And if you skip any single clue, two suspects survive, so you needed all four. That’s how you know a puzzle is playing fair.
Did Hugo’s 7:30 catch you out? Words like after, before and not are where most beginners slip. Read them twice. We’ll practise them properly in Part 4.
Three habits to take with you
- One clue at a time. Finish a clue completely before you start the next.
- Cross out, don’t circle. Your job is to remove the innocent. The guilty one is whoever’s left.
- Keep a ledger. Write how many suspects remain after each clue. If a number ever looks odd, you’ll know exactly where to look back.
Coming up at Detective School
- What is a murder-mystery logic puzzle? (you are here)
- Reading the case file: the clue types you’ll meet
- The grid made simple: who, where, what and when
- “If… then” clues and “not” clues
- Timelines and alibis
- Contradictions and the liar clue
- Checking your answer (and the joy of the reveal)
- Murder-mystery game night with friends
Ready for a real case?
When eight guests feel like a warm-up, try a whole manor house. In The Missing Guest List, the guest list has gone up in smoke and you rebuild the truth from the household’s records, clue by clue, until only one name can stand. It starts with a practice puzzle, it has hints if you get stuck, and you can check your final accusation, spoiler-free, on the Check Your Accusation page.
And for a quick daily warm-up, there’s always the free Daily Cryptogram.
Want new cases before anyone else? Join The Case File Letter, my little dispatch of fresh puzzles and book news.
See you next Friday for Lesson 2. Bring a pencil and your suspicious face.
— Ivy
Ready for a real case?
Try today’s free Daily Cryptogram, or pick up a casebook.