Summary. It was Xerxes who did it, and not for the will nor for any quarrel over the Colonel's favour, but because he came upon a thief in his own corridor and put her down for it. He had stepped out from the music, he found Effie Strange with his companion's jewel in her hand, and he shot her and took it back. Here is how I came to it.

The Reckoning. The method wants no great cleverness, only nerve, and Xerxes had that in plenty. He drew one pistol from the Colonel's cased pair in the gun-room off the corridor — the case was found later unlatched, its fellow gone — and during the covering dark of the second nocturne he excused himself to look in on Aziz, who kept to the guest apartment unwell. He did not go to Aziz. He met Effie coming out of that same apartment with the Sapphire in her hand, and he shot her once, and put the jewel back in his pocket, and set the corridor to rights before he went down again. He was in his chair as ten o'clock struck, unhurried, as he is in most things.

The Colonel I set aside first, and gladly, for a man cannot shoot from a chair his neighbours swear he never left; he sat facing the piano throughout, and stirred for nothing until the candles were relit. Nan stood the whole time at the lit stand, in view of the company, and never quit her post until the alarm was raised — no darkness covered her. Below stairs Fifi was laying supper under Mrs Gow's eye and never came up at all. Zane stood at the drawing-room doors the entire evening, placed there by the housekeeper and two of the guests besides, and a man cannot mind a door and a corridor both. Each of them wanted only the ordinary courtesy of being looked at by someone else at the hour it mattered, and each of them had it.

The motive, when it is put plainly, is a shabby one, and shabbier for being so small beside what it cost. Effie owed money about the town and more besides to her laudanum, and she had long admired the Sapphire Aziz wore — a gift Xerxes had made him, of a kind the household did not discuss and I shall not discuss either, save to say it ran deep and was not lightly crossed. She judged the darkened music her chance and took it, meaning only to relieve a man too ill to notice her enter. She had not reckoned on meeting the giver himself in that corridor, nor on what the taking of that particular stone would mean to him. He did not call for the watch, nor rouse the house. He judged her a thief and settled the matter as such men settle matters, with no more ceremony than a man closing an account.

I had near forgot one small thing, though it wants noting: her gloves, laid beside her neatly, not dropped in any struggle. A thief surprised does not compose herself so; a man who has already decided what must be done, and is not shaken by the doing of it, will tidy even a corpse before he goes back to his chair. That is Xerxes entire, and it is what closes the file. The third this twelvemonth, by my count, and I have charged him accordingly.

When all's said and counted, the deed it was done,
and Xerxes the answer, when answer was none.
Poor Effie 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.