These late stories by Wilkie Collins are not strictly mysteries, although they contain crime elements. The form of the classic detective story had not yet evolved, saving for the Dupin stories by Edgar Allan Poe. Many Victorian novels, however, were mysteries, involving official police or private investigators, and a crime of some sort often with melodramatic and Gothick turns of plot -- including Collins's own The Moonstone (1868). The Haunted Hotel is basically a ghost story with a sub-plot involving a cleverly contrived murder. And My Lady's Money is a social comedy involving a theft and a wrongly suspected person.
Wilkie Collins by this time was seriously afflicted with gout, poor vision, and other ailments, and he was heavily addicted to laudanum. His works of this period were generally poor and did not sell well. It is remarkable that he was able to write these two short novels in such a readable fashion. Plot, wit, and atmosphere are almost at the level of his earlier masterpieces.
The Haunted Hotel is mainly set in Venice, in the winter, invoking an eerie setting much like that of Daphne DuMaurier's Don't Look Now (or rather, the fine movie version by Nicholas Roeg). The mystery occurred in a decrepit, decaying palace, involving a miserly and hermitic Irish nobleman, Lord Montbarry, his adventuress of a wife, Countess Narona, her wastrel scoundrel of a brother (perhaps also her lover), and a personal courier such as the wealthy often hired as private tour guides. Lord Montbarry dies in the palace of bronchitis, and the courier vanishes without a trace. After Lord Montbarry's death, a syndicate including many members of his lordship's extended family was set up to buy and renovate the palace as a first-class hotel. One of the rooms seems to be haunted, but only to members of the family who stay in it, not to other guests. The plot continues in a well-constructed manner until the quick and melodramatic denouement. Countess Narona is one of Collins's characteristic enchantresses, obsessed with fate and hence self-destructive, her own worst enemy. She writes the synopsis of a dramatic play -- obviously based on real people and occurrences -- typical amateur behavior, and a rather weak and unconvincing aspect of the story, although the theatrical background is amusingly satiric. There is also a life-insurance fraud in this tale, perhaps the earliest use of this theme. On the whole, this short novel is a pleasure to read, even if it does not reach the heights of Collins's earlier achievements.
Note: This story contains the first definition of 'brain-dead' that I know of: "Is she likely to die?" "She is dead ... of a rupture of a blood-vessel on the brain. Those sounds [stertorous breathing, etc.] you hear are purely mechanical -- they may go on for hours."
My Lady's Money is written in a much ligher vein, and has no murder but rather a theft of a large banknote from Lady Lydiard by a person whose identity is pretty obvious to the reader -- but give Collins credit for creating additional suspects who are the center of attention in turn, a practice later commonly used by mystery writers. The apparent culprit is Isabel Miller, who had the most obvious opportunity to steal the banknote from an usealed letter, but Robert Moody, milady's steward, having a romantic interest in the girl, is not satistfied and hires an investigator. The detective is called Old Sharon. He is a run-down tramp-like disbarred lawyer, an interesting character and an early version of the 'anti-detective'. ("Entering the room, they discovered, through a thick cloud of tobacco-smoke, a small, tat, bald-headed, dirty old man in an armcharir, robed in a tattered flannel dressing-gown, with a short pipe in his mouth, a pug-dog in his lap, and a French novel in his hands.") This is a very light-weight story, yet it is entertaining and definitely worth reading for aficionados of early mysteries.
Note that the close-mouthed lawyer, Mr. Troy, appears in both books. He would have made a good 'series' character. There's an idea for some would-be Collins pastiche artist. Troy is in some ways a forerunner of R. Austin Freeman's Dr. Thorndyke (or rather his lawyers like Anstey and Brodribb).