Summary. It was Nan, the poor relation who is nowhere and everywhere in that house, and she did it because Cousin R had begun to see her — here is how I came to it.

The Reckoning. The cause was an omission, not an act, and the household's own good order made it plain. A general caution had gone round the table that the back stair stood unlit, its gas off, its bar removed — Quill himself had repeated it to the drawing-room party. Cousin R came late and was not at that table to hear it. When he rose to fetch his own bottle, as was his fond little courtesy, the short way lay down that stair, and no one thought to tell him privately what the room already knew. Someone should have. Someone who knew the house in the dark as well as she knew it lit did not. He went down by a stub of candle that had already begun to gutter, missed his footing at the cellar step, and broke his neck in the fall. There was no mark on him otherwise, no staging, nothing posed — because nothing had been done to him. The whole of the killing was a silence.

The Colonel never left his whist chair from the moment R rose until the body was found, the three other players and Mrs Gow's tray all placing him there entire. Xerxes sat the same rubber through, under the same eyes. Lady Lavinia was continuous in the small drawing-room, Mrs Gow coming and going with trays the whole while, and Quill sat with her party, having himself broadcast the very warning R never heard — a man does not withhold a caution he has just spoken aloud to a room. Fifi was belowstairs in the kitchen passage, vouched by Mrs Gow; Zane was carrying the whist tray up and down at the front of the house. None of them were anywhere near that back landing in the window that mattered, and the farther-off names — the Captain aboard, Aziz at Hartfield, Effie at her card-party, the Reverend at his own church — never come near the house at all.

That leaves the poor relation, Nan Pringle, who is resident, who is never remarked, and who alone was as much at home in the unlit back passages as at the whist table. It is worth recalling — I had nearly set it down as a mere household detail — that hers was the one presence equally natural in both places that night, which is precisely why no one thought to notice whether she had gone from one to the other.

As for why: Cousin R was known through that house as a cold, fixing sort of watcher, the kind whose attention, once caught, does not slide off a person the way most men's does. It had caught, more than once, on Nan — followed her about a room in a way that had begun to be remarked belowstairs. A woman whose whole safety lies in going unseen cannot buy off such a man, cannot ally with him, cannot outwait him. She can only be rid of the eye. She said nothing, at the one moment when a word would have saved him, and let the dark and the stair do the rest.

I do not think she raised a hand to him, and the coroner will find none. But a caution withheld, by the one soul who knew it was needed, is a killing all the same. I charge her with it. The third this twelvemonth, by my count, and the year not out.

Nan mixed the household's evening brew with care,
And Cousin R came down the stairs to dare
The cellar's depths where bottles lay in wait,
But none had warned him of the lightless gate—
The moral here, we're certain, must be plain:
Keep watch, keep word, or loose what you might gain.