The door gave a finger's width and stopped. On the wall of the hall is the history board the rental company put up, and every name on it is a name you know.
Hour Two: the accusation

The rental company's history board hangs by the stair, brass letters on oak, the kind of thing guests photograph:
SALLOWMERE HALL
1612 great stair built
1665 shut up in the
plague year: the
Hale household
1912 bought by Edmund
Locke
1941 requisitioned
1998 sold
2026 restored
Under it, somebody has pinned the host's messages from the week, printed out, as if for you. You read them in order:
night 1 Thank you for
keeping the fire.
night 2 You remembered
where you put the
key. She is pleased.
night 3 You stopped them.
She knew you would.
Every one signed P.
On the hall table, where the glass case was, somebody has laid out the cards of the old country-house murder game from the cupboard in the dining room, sixteen of them, face up, the way the game ends: a person, a room, and the thing it was done with. Only these cards are not the game's. They are this house's.

Make the accusation the way the old game does: who, in which room, by which light. Tap them in that order.
The accusation: nothing yet
Look again at what the host has thanked you for, all week, and at where the knocks came from.