How a case works
The board is a square grid, usually between 5×5 and 8×8, cut into rooms by thick walls. Rooms have names, like the Library or the Cellar, and some cells hold furniture or scenery. A person can stand on a chair or a bed. A plant or a table blocks its cell.
A case has as many people as the grid has rows, and one of them is the victim. Each person comes with one or two clues written as plain facts: "She was in the top row." "He was beside a plant." "She was not in the Kitchen." No clue is a lie, and none is there for decoration.
The one rule borrowed from sudoku does most of the work: no two people share a row or a column. The last rule turns the grid into a crime. The victim was alone in a room with exactly one other person, and that person is the killer. You never accuse anyone on a hunch, because the full board tells you who it was.
Every case on this site has exactly one solution, and a solver checks that you can reach it by deduction alone. The exact meaning of every clue is on the rules page.
How it differs from killer sudoku
The names sound alike, so search results mix them up. Killer sudoku is a number puzzle: a normal 9×9 sudoku where dashed cages show the sum of the digits inside them. It is arithmetic from start to finish, and "killer" only describes how hard it gets.
A murder sudoku has no digits and no sums. It keeps the row and column rule and adds rooms, objects and a culprit, so you lose nothing if you have never solved a sudoku. The two are compared in detail on murder sudoku vs killer sudoku.
Three puzzles side by side
| What you place | Main rule | Clues | Arithmetic | The answer | |
|---|---|---|---|---|---|
| Murder sudoku | People on a floor plan | One person per row and column | A fact per person: "He was beside a plant." | None | The killer |
| Sudoku | Digits 1 to 9 | Each digit once per row, column and box | Some digits given at the start | None | A full grid |
| Killer sudoku | Digits 1 to 9 | Each digit once per row, column and box | A sum for each cage | All the time | A full grid |
Murder sudoku
What you place: People on a floor plan
Main rule: One person per row and column
Clues: A fact per person: "He was beside a plant."
Arithmetic: None
The answer: The killer
Sudoku
What you place: Digits 1 to 9
Main rule: Each digit once per row, column and box
Clues: Some digits given at the start
Arithmetic: None
The answer: A full grid
Killer sudoku
What you place: Digits 1 to 9
Main rule: Each digit once per row, column and box
Clues: A sum for each cage
Arithmetic: All the time
The answer: A full grid
The kinds of clue
Every case is built from seven kinds of clue. Each has its own page with examples from the game. Clue types
- In a room: "She was in the Library." The person is somewhere inside that room.
- On an object: "He was on a chair." The person sat, lay or stood on that kind of object.
- Same row or column: "She was in the top row." The person is somewhere on that line.
- Beside an object: "He was beside a plant." Next to it, side by side, in the same room.
- In a corner: "She was in a corner of the room." A cell where two of the room's walls meet.
- Alone in the room: "He was alone in the room." Nobody else stood in his room.
- With another person: "He was in the Study with another man." The room, and exactly one other man there.
Try a small one
A 4×4 case with four people, one of them the victim. Pick a person, tap a cell, and submit when everyone is placed.
The victim. He was alone with the killer.
Pick a suspect, then tap a cell.
Play this case and the whole casebook in the app, free on iPhone, iPad and Android.
Where the genre comes from
The puzzle joins three older traditions. Logic grid puzzles go back at least to the zebra puzzle, a list of facts about five houses that a magazine printed in 1962. Number place grids, the puzzles that became sudoku, appeared in American puzzle magazines in 1979 and got the name sudoku in Japan in the 1980s. The country-house whodunit, with its closed rooms and short list of suspects, is older than both.
In recent years puzzle books and apps started to merge them: a sudoku-style grid drawn as a floor plan, people instead of digits, and a body in one of the rooms. Different makers use different names and slightly different rules, for example how many people may share a room or whether "beside" includes diagonals. Our rules page settles each of those, so a clue never has two readings.
Why people like it
A case is short. An Easy 5×5 takes a couple of minutes and a Hard one ten or more, which fits a coffee break, and the daily case gives you a reason to come back tomorrow.
It also has an ending. A number puzzle stops when the last cell is filled. Here the last placement names someone, and the case is stamped closed. If you read detective stories you get the reveal, and if you only care about logic you get a puzzle that never asks you to guess.
The clues are plain sentences, so there is no notation to learn first. You can solve a first case without reading the rules, and the technique pages help once the Hard cases start to push back.
Where to play
A new case comes out every day at midnight UTC, free in the browser and the same for everyone: today's case. Monday and Tuesday are Easy, and the week climbs to Expert on Saturday. Past days stay playable in the archive, each with a worked solution. To learn the rules with a practice case, start with how to play.
Put it to work on a real case
A new murder at midnight UTC, free in the browser, with one arrangement that fits every clue.