"Markheim" is a short story by Robert Louis Stevenson, originally prepared for the Pall Mall Gazette in 1884, but published in 1885 in The Broken Shaft: Tales of Mid-Ocean as part of Unwin's Christmas Annual.
A man named Markheim has come even though the store is officially closed, and the rather shady dealer points out that whenever he comes to visit after hours, it is usually to privately sell a rare item, claiming it to be from a late uncle's collection he inherited.
Markheim visibly flinches at the dealer's not-so-subtle insinuations, but claims that he has not come to sell anything this time, but rather to buy a Christmas present for a woman he will soon marry, implying she is well off.
Surrounded by mirrors and ominously ticking clocks, and with only a candle to light up the dark shop, Markheim spends some minutes recovering his nerve when he hears someone moving about upstairs, though he knows the dealer's maidservant has taken the day off and no one should be there.
The servant returns, and as she knocks on the door, the stranger advises Markheim that he can entice her in by telling her that her master is hurt, then kill her and have the whole night to ransack the house.