Summary. It was Xerxes, master of Hartfield House, and he killed to keep a stone and its meaning hidden; here is how I came to it.

The Reckoning. Effie Strange died of one ball through the breast, fired at close range while the fountain's noise covered the report, and there was no second shot because none was needed. She had gone to the fountain's edge to pull the glove from her hand — the better to work a fastening — and had lifted Aziz's jewel from wherever he had left it, meaning to pawn it for laudanum money, as she had lifted smaller things before her. She was caught in the act. The empty slip-case beside her, and the glove dragged off in haste, tell that part of it plainly enough; her own reticule, untouched, tells that robbery was never the object, only the appearance of one. Whoever shot her did not want her money. He wanted what she was holding, and he wanted the matter never spoken of again.

The house offered robbery and rivalry both, and neither survives an hour's asking. Aziz cannot have done it — he was dressing across the house, his valet swears to the hour, and in any case the stone is his own; a man does not rob himself and shoot the thief for the privilege. Wat had no cause; Effie was a paying customer, and he stood at the water-stair with two boatmen through the whole of the report. The Colonel and Nan clear each other, being together in the library with the clerk between them, and besides that, the will was unsigned — no favour had tipped, so Effie was not yet a rival worth killing. Lavinia had two maids at her elbow laying out a table for spirits, and a mocked medium's grudge is thin stuff beside a bullet. That leaves the pistol, which any diner might have taken from the vestibule, and the man who alone had reason to want the jewel back and the reason for its theft never aired.

The jewel is not merely valuable. It is the one thing Aziz wears openly that says, to anyone with eyes to read it, what he is to Xerxes and what Xerxes is to him — an attachment of long standing, of a kind this household has never once put into words at dinner. Effie did not understand what she had taken, only that it was worth money. Xerxes understood it very well. Caught her with it in her hand at the fountain's private end, out of sight of the drawing-room doors, he did not think long. He took down one of the pair of duelling pistols that hang where every guest may see them, fired once while the water swallowed the sound, and put the gun back fired into its case. He left the stone where it had fallen among the ferns rather than be seen stooping over her, and recovered it quietly afterward, when the house had gone in for its supper and its shock. It was never robbery. It was never the Colonel's will, nor Wat's debt, nor Lavinia's wounded vanity. It was a man protecting the one public sign of a private truth, and a woman who picked the wrong bauble on the wrong evening. The third this twelvemonth, by my count, and I am charging Xerxes with all of it.

Xerxes chose the hanging gun, and made the evening plain
And Effie met the fountain at the edge of the rain
A single shot went softly where the falling water streamed
The empty slip-case waited, and the household only dreamed
The moral, guard your secrets as a prudent person should
We'll practise this tomorrow—if we find it rather good