Summary. It was the Colonel, and he killed his own partner to keep whole a venture he had that evening learned he could not have kept half of — here is how I came to it.

The Reckoning. The dinner told him the thing before the pistol did. He carried in the Bombay letters himself at 8:45, between the fish and the sweet, and read at table what the factor's quarterly letter said in plain figures: that the Cairnholm end had been carried three years by the Bombay end, and that the partner who found the money and the trade meant, within the month, to say so, and to place his agency at Liverpool instead. A man does not go the colour of his collar over a remittance. Nan set it down as unusual because it was; her book has never yet recorded him wrong. He said nothing further at table, rose with the rest at 9:00, and did not go out to the carriage sweep, whatever he told the household afterward — his own man, who had stood by the horses since 8:00, says plainly that he never came. What he did instead was go along to the writing room, with one of his Sunday pistols in his coat, as he goes about at night from long habit, and put an end to the arrangement before the arrangement could end him.

The room itself keeps a fair account of the four minutes. He tore the accountants' schedule out from beneath its Glasgow covering letter and burned it, though a scrap of foreign wrapper beside it declined to take the flame and so survived to be found; that valuation was his own commissioning, and no one else in the house had cause to be rid of it. He wrenched the lid from the sandalwood box to get at the venture books, not to steal them — they were left open on the table, quite unharmed, two pages unpinned and compared as a man compares a thing he already suspects. The quarrel was short and loud, and he shot Xerxes from the doorway side at some six feet, which is Dr Quill's finding and fits no other hand in the house. Going out he knocked a heap of letters to the carpet and unlatched the window to suggest a thief come in from the mud — mud that took no boot-print at all, the drop being eleven feet and the sill soft. He was back in the hall by the alarm at 9:20, the pistol still in his coat, and no pistol was ever found because it never left him.

The rest of the house falls away on plain grounds and costs little ink. Nan was in the morning room with Lavinia and Gaunt from a minute after the rising until the alarm, the three never parting, and her only offence was a book kept honestly. Wat was in the kitchen passage taking a brandy he had to beg for, watched by a reluctant cook and stepping the whole time round a cheetah that never stirred for any other crossing — and besides, Xerxes dead is Wat's living ended, not advanced. Aziz went up before the table even rose and was on the landing with the housemaid Duff at the very minute of the shot, counting heaps he had no pistol and no house-custom of pistols to bring to any quarrel. Lavinia and Gaunt vouch each other and are vouched by Nan, and neither had a shilling nor a grievance in the Bombay letters, which were none of their affair. The twins were at the Manor under the household's eye, Effie was dancing in company at the Assembly Rooms, and Cousin R was under a night porter's nose at the station hotel.

That leaves the Colonel unlocked, and everything about the room points at him and no other: the pistol pattern Quill describes, the accountants' valuation he alone had ordered and alone had cause to burn, the venture books opened and compared rather than taken, and a habit of the sweep he has never in eleven years actually kept. He believed, on the strength of one evening's reading, that he was the dependent partner and about to be shown the door of his own concern — and he believed, wrongly and fatally, that removing the man who could prove it would leave him the whole machine to run alone. It will not run alone now. He is charged, and the file may close — the third such closing this twelvemonth, by my count, though I own I have lost the thread of the tally somewhere behind me.

The Colonel dined at eight and wore a most considered frown,
While Xerxes read the venture books before the lamps went down.
The fire consumed a covering, the box surrendered its key,
And someone opened up the sash to blame the outer lea.
We learn that greed is dangerous, and very bad for trade,
Then keep the books beneath the lock and ask to be obeyed.