A Halloween mystery: how to run a deduction night at home

Why a deduction case works on a night like this

Because it does the three things you need when the house is full and nobody wants to read a rulebook.

It explains in five minutes. One person per row and column, the cards tell the truth, and whoever ends up in the victim's room is the murderer. That is the lot.

Everyone starts at once. No turns, no dice, nobody waiting for anybody. Whoever turns up late sits down and plays.

It ends. A case lasts about as long as a conversation, has exactly one solution and can be checked. Nobody is left feeling the game stretched itself out.

And the subject matter is the subject matter of the night: there is a body, and somebody has to be named.

What you need, and what you do not

You need a printer, pencils and a table. That is it.

Printable cases are free and need no sign-up. Each comes in color, in black and white — the one to use if you are running off eight copies, because it does not eat the ink — and with the solution as a separate PDF, which is exactly what you want with people around: you hand it out at the end.

You do not need costumes, an app, or anything prepared the night before. And if you have no printer you can play in the browser, passing a phone or tablet around, though in a group paper wins: everyone crosses out their own squares.

The format that works best: a detective race

Print the same case for everybody and hand it out. Pairs beat playing alone: the fun is in listening to people argue.

One rule changes everything: you do not win by naming the murderer, you win by justifying it. Whoever raises a hand has to explain the first step — which card they attacked first and why that one — and if it does not hold up, the race carries on. Without that rule, somebody guesses right in three minutes and the evening is over.

When the last pair is still going, give them the solution and have them read it out loud: it comes with the reasoning written alongside, not just the filled-in grid. That is the moment somebody says "oh, of course" and asks for another one.

Three variants, depending on the room

Teams, out of earshot. Two teams in different rooms with the same case. First to come back with the name and the reason wins. It gets loud.

Round the table. One case in the middle and one-minute turns: each person crosses out one square and says why. It moves slowly and everybody follows, which is what you want if there are children.

Easy to hard. Start with a small case so the rules land by playing, then bring out a big one for whoever wants to stay. The ones who tire drift to the kitchen and the ones who do not have their evening sorted.

The settings that give you the atmosphere

This year there are cases tied to the night, three of them: they take place in a haunted mansion, with the suspects in costume, and they are on the printable cases page.

Even so, you do not need pumpkins on the page for a case to carry the night. The atmosphere comes from the place: a mansion, with its corridors and drawing rooms; a forest; a museum after closing time; a swamp; a cave; a night train.

It is exactly the set of an old-fashioned mystery novel, which is what the night is asking for. And since every case comes with its floor plan drawn, you can leave it on the table as part of the decoration.

With children, and with adults who play like children

With children, take a small case with few suspects: it solves in a few minutes and the reasoning can be read out together. And explain what "next to" means before you start — the adjacent square, inside the same room; walls cut — because it is the one rule that gets misread.

With adults the problem is the opposite: somebody will try to solve it in their head without crossing anything out, get stuck, and announce that the case is broken. Leave pencils within reach and make them cross out. It is solved by ruling out, not by guessing.

And if somebody likes it too much: the book

There is always one who asks, at the end of the night, where there are more. The answer is Sudoku Detective: a paperback, in full color, with illustrated settings and the solution to every case explained step by step. It is the kind of present that actually gets used, and it lands as well at Halloween as at Christmas, which is right behind it.

The cases in the book are its own and are not on the website. In the meantime the site is free, with new cases every week, and the full rules are here with one case solved end to end, in case you want to read them before anyone arrives.