Summary. It was Dr Quill, and for no gain at all but his own fright; he took a warning meant to guard another man's secret and heard in it his own death sentence, and so went into the glasshouse and pressed Aziz's face into the wet peat until the thing he feared could not be done to him. Here is how I came to it.

The Reckoning. There was no wound on the man, and no poison touched, though the border stood four paces from where he died with every brass label in its place. That told me at once what the case was not. A poisoner with the whole of that collection at his elbow, and untouched, is a poisoner with no wish to be read as one. Dr Quill's own bag lay open on the bench nearby, instruments in order, nothing gone from it — the ablest hand in Cairnholm for such work, and he used none of it. He used his hands instead, clumsily, and left the glasshouse to show it: pots over, gravel scuffed, a label knocked from its stake, the fez struck off into the walk. Nothing tidied, nothing posed. A man who plans a poisoning does not leave a room looking like a scuffle. A man surprised by his own nerve does.

The emerald settled the matter of motive before I had one. It hung on the body in plain sight, worth more than any servant in that house will see in a lifetime, and nobody had troubled to take it. Whoever did this wanted nothing Aziz carried. That put paid to Wat Frew directly, whose quarrel that week was cargo and freight shares and nothing to do with the dead man, and who besides was in the wine cellar with the butler from twenty minutes to eleven until the alarm, both their hands on the tally sheet at a quarter past to prove it. It put paid to Lavinia too, who wanted Xerxes's continued generosity and gets none of it by Aziz's death, and who sat at the drawing-room piano from ten minutes to eleven before eleven witnesses who had no cause to look elsewhere. And it put paid to Gaunt, who had not exchanged two words with the dead man in as many years and was in the porter's lodge disputing scripture when it happened, the porter his witness and his gaoler both.

That left the physician. Dr Quill had been put back down the west stair by Aziz himself, before two servants, and told plainly that a man who wandered in that house would be carried out of it. He is a nervous man by temperament and a careful one by trade, and he took the words for exactly what they were not — a sentence passed on him, rather than a warning meant to keep strangers from a door that was never his business. He asked the apothecary's wife, within the week, whether the law could touch a man for what he had not yet done. That is not the question of a man reassured. He sent the draught up by a boy twice rather than climb that stair himself. On the night, he left the drawing-room at five minutes to eleven pleading the heat, and was not seen again until he came in of his own accord at eighteen minutes past to raise the alarm — the first medical man on the scene because he had arranged to be. His cuffs were wet and stained brown when the company gathered round him, which he had not troubled to explain, and which wanted no cleverness to read: he had washed his hands in the trough water where he'd held Aziz down.

As for what Aziz was guarding on the west landing, and what he was to Xerxes that made him guard it so fiercely he'd turn back a housemaid with the tea things — that is the two of them's own affair, settled long before I was called to the house, and none of my business to set down in a police file. It is enough to say that the closet, and the man who kept it, meant everything to Aziz and nothing at all to anyone else in that household but the one man it protected. Dr Quill did not understand that. He understood only a threat, made in temper, by a frightened man who never meant it as one. I have charged him accordingly. This makes the third this twelvemonth at that house, by my count, and I confess I had rather hoped not to be sent back.

It fell out, in the end, as the cruellest of fate,
with Quill 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.