Summary. It was Cousin R, the Colonel's long resident guest of no fixed relation, and he killed her not for what she knew of others but for what she gave to him alone — because she had spent four months feeding a private collector everything she overheard in the two houses, and had just announced she was leaving Cairnholm for Perth within the fortnight, ending the supply and taking what she knew of the collecting out of his reach.

The Reckoning. The mixing itself is plain enough. The negus went up from one bowl at 9:15, split to two trays, and the gallery tray harmed no one, which clears the bowl and Mrs Gow's kitchen entirely. The staff tray held four glasses, and three were drunk without consequence; only Fifi's, carried the four paces into the linen room that was hers and no one else's, held the dose. Whoever poisoned her needed only to know which glass was Fifi's and to have the run of the back landing alcove between half past nine and a quarter past ten, when Dr Quill puts the taking of it. Cousin R left the gallery twice in that window, each time pleading the incense, and each time returned. No one else in the house crosses that corridor at all.

The others fall away on plain fact, not on character. Xerxes was shut up with the Colonel's clerk over the subscription papers from 9:20 to 10:10, the clerk swearing to it and the papers initialled at every foot; he never came near the alcove. Aziz sat the whole sitting out at draughts with Zane in the front hall, under Mrs Gow's eye four times over; he never entered the gallery corridor at all. Lavinia sat the chain from nine to a quarter past ten with the Colonel holding one hand and Nan the other, and the séance wants an unbroken chain — she could not have crossed the room, let alone the landing. That the line against Zane's name was scored through and through tells its own story: whatever else Fifi traded, her brother's business she kept, and Lavinia had nothing to silence her for. Gaunt was at his vigil in Kirkwynd from eight till midnight, before his own verger, and never set foot in the Manor that evening.

The apron list looks, at first handling, like a blackmailer's ledger, and the household read it so — a dangerous girl, hinting at Hartfield House, struck down by someone with a secret to keep. It is nothing of the kind. It is an inventory, kept by a girl proud of her trade, of everyone she had something on. The true ledger sits upstairs, in the blue bedroom, in a commonplace book eleven years in the keeping, thickened in the last four months to a dozen entries a week where once it managed a dozen a year, and sourced almost entirely to a single initial. The Thursday hour in the linen room was not courtship, whatever the servants' hall made of it laughing; it was collection day. What passed between them beyond that — call it an attachment of a peculiar and one-sided cast, the sort a decent house does not examine too closely — is his affair. What it drove him to is mine. When she announced on the Wednesday that she was for Perth within the fortnight, she ended the arrangement on her own terms, and Cousin R does not care to have his material end on anyone's terms but his. He measured an exact dose into hot spiced wine, set nothing right and nothing wrong in the room after, and let her die tidily in her own chair, which was, I think, very much how he preferred to remember her. I have written to have him held. It is the third this twelvemonth, by my count, and I do not expect it to be the last.

When all's said and counted, the deed it was done,
and Cousin R the answer, when answer was none.
Poor Fifi lies quiet, a candle, a knife,
the tidiest exit from Cairnholm and life.
The lesson is here, should we trouble to learn —
but the cards, being cards, will be dealt a fresh turn.