Summary. It was Effie, and for the ring on Aziz's chain — here is how I came to it.

The Reckoning. The dose went into the sweets nearest the foot of the table, where Aziz always sat, and into his champagne besides; the laudanum came from Dr Quill's case, but the case stood the evening in an unlocked hall cupboard that three of the party had already remarked upon at dinner, so it was drug common to the house and no mark against its owner. Aziz went up heavy at a quarter past nine. From half past nine the seance held the rest of the table in a circle that Lavinia's own rule required to be unbroken, and it was not broken — Gaunt, the Colonel, Nan, Quill, Cousin R, each accounted for by his neighbour's hand from a quarter to ten until ten past eleven. Captain Frew's one absence was ten minutes in the hall over a telegram, in the hall boy's sight, and the light and the humming in the writing-room were reported at ten o'clock, before he stirred; ten minutes will not carry a man up, along, and back. Xerxes went only to the stair-foot, in view of the circle throughout, to quiet the cheetah, and the beast's rising at that hour is the whole of his movement accounted for. None of these had reason besides. Gaunt's old acquaintance with Tangier was never spoken of in his hearing; the Colonel had got his codicil signed and was well pleased with it; Nan touches the Colonel's figures and no money of her own; Cousin R disturbs nothing in a room, and this room was left exactly as it fell, cushion on the floor, fez set aside by a dying man's own hand.

Effie alone was not in the circle. She had said at table she preferred the fire to the dark, and a housemaid saw her settled in the library at twenty minutes to ten — and saw her again, composed, in the drawing-room doorway at ten past eleven, when the lamps came up. Between those two sightings lies the whole of the business. She went up at about ten, found Aziz insensible where the dose had put him, unhooked the chain without breaking the clasp, took the ring, and finished the work with the velvet cushion, quick and without flourish, a woman who has done harder things than this for pin money. She came down again, wiped and emptied the one saucer that mattered, and burnt the lining of a jeweller's slip-case on the library hearth against the very fire she'd claimed to want. It is not much to look at, that scrap of scorched velvet, but there is no slip-case anywhere in the house, and a jeweller in the Candleriggs opens his door at eight the next morning and asks no questions of a loose stone.

As to why: her credit in Cairnholm was closed since Lady Day, and her father's codicil, signed the day before and read out at table with such satisfaction, closed the last door she had any hope of walking through honestly. She had asked Aziz for that ring once already, in April, and been refused; it was the one thing in the house he would not sell, being Xerxes's own gift and worth nothing to him but its giving. That left only taking it quietly — and Aziz caught her at some earlier mischief upstairs and told her plainly, in the hall before dinner, that he meant to tell the master of the house. A woman who has already resolved to steal does not stop for a witness. She stopped him instead. The ring is not yet found, but it will be, at a Candleriggs bench or in whatever hem she has sewn it into; the account otherwise wants nothing further. I have laid the charge. It is the third this twelvemonth, by my count, and I confess I am tired of this house and its dead.

It fell out, in the end, as the cruellest of fate,
with Effie the reason, and reason came late.
Now Aziz is gathered, a held, careful breath,
one more of the twelve to the ledger of death.
The moral, we're certain, is worth the whole cost —
then shrug, and forget it, and reckon naught lost.