It is the year 1890, the month of November, and Sherlock Holmes is rapidly recovering from three days and nights of starvation, part of an elaborate ruse to trick a murderer, in “The Adventure of the Dying Detective.” Only a few weeks before that, he had solved the ingenious mystery of “The Red-Headed League.” His friend and chronicler, Dr. Watson, no longer lives at 221B Baker St., having wed Mary Morstan, whom he met two years previously in “The Sign of the Four.” But, as “The House of Silk” opens, Mrs. Watson has just left for a stay with friends in the country, and her husband has, temporarily, moved back into his old rooms.

And so the stage is set for one of the greatest cases of Victorian England’s greatest detective.

There are 56 short stories and four novels in the established canon of the Sherlock Holmes adventures. But Dr. Watson tantalizingly alludes to a number of others, “for which the world is not yet prepared.” Recall some of their titles: “The Giant Rat of Sumatra,” “The Politician, the Lighthouse, and the Trained Cormorant,” “The Amateur Mendicant Society” and “The Singular Adventures of the Grice Patersons in the Island of Uffa.” Don’t they all inspire reverie and speculation? (Note, for instance, the word “in” rather than the expected “on” in that last case. Is that significant? Holmes constantly reminds us of the importance of trifles.)

Many of these unpublished cases repose in a safe-deposit box at Cox and Co. in Charing Cross Road. Among them, till recently, was “The House of Silk,” characterized by Watson as “simply too monstrous, too shocking to appear in print.” He adds that full knowledge of the facts “would tear apart the entire fabric of society.” Writing in what must be 1915 — when the great detective is dead and his elder brother, Mycroft, retired — Watson announces that he is leaving instructions that his account of these horrors remain sealed for 100 years.

Somehow, though, Anthony Horowitz — well known as the author of the Alex Rider novels for young people and the scriptwriter for a number of British television series (most notably “Foyle’s War”) — managed to free the manuscript a few years in advance of that century mark. All readers and Sherlock Holmes fans will be grateful that he has.

“The House of Silk” opens when a rather foppish art dealer comes to Holmes because he feels in danger from a silent, mysterious man who wears a distinctive flat cap and bears a livid scar on his face. Who could this ruffian be? Edmund Carstairs eventually relates an extraordinary story involving a train robbery in America and a shootout with a notorious gang led by a pair of Irish twins. Carstairs is convinced that a survivor from that shootout has marked him for revenge.

But is this supposition correct? On his voyage back from America a little over a year before, the traumatized Carstairs met and soon married an attractive widow named Catherine Marryat. Some of his servants regard her as bringing a needed breath of fresh air into the rather stiff and sorrowful Carstairs household. The art dealer’s mother has just recently died, his spinster sister has grown increasingly paranoid, and one Irish serving boy has even begun to behave in a sullenly provocative manner. Something is clearly amiss. Yet why does the great detective chiefly want to know if Mrs. Carstairs is able to swim?

Before long, Holmes and Watson call in the street urchins known as the Baker Street Irregulars to help locate this elusive and threatening American, at which point what had seemed a relatively simple affair starts to grow increasingly byzantine and dangerous. A frightened young slattern mentions “the House of Silk”; a body is found horribly tortured and mutilated; Mycroft Holmes — who sometimes “is” the British government — strongly warns his brother off the case; and one night Watson finds himself the guest of a certain reclusive professor of mathematics, highly esteemed for his groundbreaking work on the Binomial Theorem.

At the climax of this exceptionally entertaining book, Holmes solves not one but three interrelated mysteries. One can only applaud Horowitz’s skill in integrating the case of the Flat Cap Gang with that of the House of Silk. His mimicking of the style and tone of Arthur Conan Doyle is equally impressive. Here, for instance, the two Holmes brothers one-up each other at the Diogenes Club:

“ ‘My dear Sherlock!’ Mycroft exclaimed as he waddled in. ‘How are you? You have recently lost weight, I notice. But I’m glad to see you restored to your old self.’

“ ‘And you have recovered from influenza.’

“ ‘A very mild bout. I enjoyed your monograph on tattoos. Written during the hours of the night, evidently. Have you been troubled by insomnia?’

“ ‘The summer was unpleasantly warm. You did not tell me you had acquired a parrot.’

“ ‘Not acquired, Sherlock. Borrowed. . . . You have just returned from Gloucestershire.’

“ ‘And you from France.’

“ ‘Mrs. Hudson has been away?’

“ ‘She returned last week. You have a new cook.’

“ ‘The last one resigned.’

“ ‘On account of the parrot.’

“ ‘She always was highly strung.’ ”

Throughout the narrative, Watson and Holmes repeatedly allude to various earlier cases, and readers familiar with the Sherlockian canon will enjoy identifying “The Devil’s Foot,” “The Speckled Band,” “The Final Problem” and several other stories. Try your luck, for instance, in pegging the possible sources for the following articles found in Holmes’s possession when he is arrested by the police: “A pair of pince-nez, a length of string, a signet ring bearing the crest of the Duke of Cassel-Felstein, two cigarette ends wrapped in a page torn from the London Corn Circular, a chemical pipette, several Greek coins and a small beryl.”

From time to time, the older Watson mentions with shame his failure to grasp the suffering of the criminal heart or to fathom the full extent of the Victorian neglect of the poor, downtrodden and abandoned. This growing understanding of social ills is not just admirable on Watson’s part, but also central to solving the mystery of the House of Silk. Setting aside some embarrassing typos and proofreading errors (Edgar Allan Poe and Mary Morstan are both misspelled on successive pages), “The House of Silk” is an altogether terrific period thriller and one of the best Sherlockian pastiches of our time.

Dirda reviews each Thursday in Style and conducts a book discussion for The Post at His latest book, “On Conan Doyle,” has just been published.


A Sherlock Holmes Novel

By Anthony Horowitz

Mulholland. 294 pp. $27.99