Solution: The Wager at Noon at the Museum

The clues

• 
  AlmaThe retired botanist.

  She was on a chair.

• 
  Greta · VictimThe gardener who talks to her roses.

  The victim. She was alone with the killer. She was on a chair.

• 
  QuentinThe butler of forty years.

  He was in the third row. He was not in the Café.

• 
  WalterThe estate’s groundskeeper.

  He was in the fourth column from the left.

• 
  OscarThe antiques dealer.

  He was in the Courtyard. He was alone in the room.

• 
  ElenaThe gallery owner.

  She was on a sofa.

• 
  BrunoThe cook who tastes everything.

  He was in the Cloakroom.

Step by step

The order our solver finds. Each step uses only the clues and what the steps before it proved, and its heading links to the technique.

1. Pinned suspects Quentin can only be in the third row, so nobody else can be there.
2. Pinned suspects Walter can only be in the fourth column from the left, so nobody else can be there.
3. Room counting The victim, Greta, cannot be in the highlighted cells: her room there could not hold exactly one other person. The cells meant: row 2, column 5; row 5, column 1; row 6, column 1.
4. Pinned suspects Greta can only be in the fourth row, so nobody else can be there.
5. Room counting Oscar was alone in the Courtyard. Nobody else can be in that room.
6. Follow it to a contradiction If Greta were in the highlighted cell, Oscar would have no cell left. So she is not there. The cells meant: row 4, column 5. Placed: Greta: row 4, column 6 (Cloakroom).
7. Pinned suspects Bruno can only be in the right column, so nobody else can be there.
8. Follow it to a contradiction If Elena were in the highlighted cell, Oscar would have no cell left. So she is not there. The cells meant: row 1, column 2. Placed: Elena: row 7, column 1 (Gift Shop); Alma: row 2, column 5 (Archive); Quentin: row 3, column 3 (Storeroom); Bruno: row 1, column 7 (Cloakroom); Oscar: row 6, column 2 (Courtyard); Walter: row 5, column 4 (Storeroom).