Who Else Was in the Room

A large family of Murdoku clues is not about a person’s tile at all but about their company. “Alone in the room.” “There was another woman in her room.” “Nobody in his room wore glasses.” “Someone in her room sat on a chair.” These clues say nothing direct about where the suspect stood. They talk about who else could have been in the same room — and that is a question about every other suspect at once.

The deduction runs like this. Take one room the suspect could be in, and ask: if they were here, could the clue be true? For “another woman in her room”, that means: is there any other woman who could still be in this room? If not, the suspect cannot be in this room. The solver phrases these steps as exactly that — someone matching had to be there; nobody can be; so not there.

Fitting, Not Just Reaching

Being able to reach a room is not quite enough for a companion. They also have to fit. Two people in one room still need a row and a column each, and in a small room that may be impossible: a box room two tiles wide holds at most two people, and only if they sit on a diagonal. If the suspect’s own tile takes the only row through the room that the companion could use, the companion does not fit, and the suspect cannot be on that tile.

This finer version catches eliminations that plain room-counting misses, and it is what the solver means when it says the required companion does not fit in the room too. It matters most in tight rooms and on clues that need the companion on an object: “a man sat on a chair in her room” fails if the room’s only chair is in the suspect’s own row.

Alone Is the Strongest Version

“Alone in the room” is the same idea from the other side. Every room the suspect might be in has to be one that nobody else is certain to be in. Once anyone is confined to a room, it is closed to everyone with an “alone” clue. And because the victim always shares a room with exactly one suspect, an “alone” suspect is never the murderer — a fact worth writing down the moment you read it.

A Worked Example

From the case Room 13: Check-In — 4×4, Medium, Hotel & Restaurant.

C1C2C3C4
R1SBC
R2CBoS
R3CB
R4C
The floor plan of “Room 13: Check-In”. Letters mark objects: C Chair, B Bed, S Shelf, Bo Box.

The clues in play:

This step comes before anyone in the case is placed, so reading it does not give the solution away.

At step 5 of the solve, the reasoning reads:

Bernd must be alone, but column 3 lies entirely in the Suite and is occupied – so not there.

Cases That Need It

59 of the 142 cases in the casebook use this technique at least once. A selection, smallest board first:

Other Techniques

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