Sherlock Holmes is retiring, and Dr. John Watson is moving into the Baker Street rooms full-time with his wife, who remains unseen throughout the film. As Holmes prepares to depart, he is visited by Prof. Moriarty, who congratulates him on choosing retirement and hints that he would have had to “take extreme measures” otherwise. Soon after, Holmes heads to the south coast of England, accompanied by Mrs. Hudson, leaving fans and foes alike to wonder if the mastermind behind a vast criminal network is truly stepping away from crime.
Back in London, Col. Sebastian Moran and Moriarty’s right hand play a dangerous game with a scheming associate, Ted Balding. Balding explains to Moriarty that he and the remaining members of the secret society known as the Scowrers want to see John Douglas of Birlstone Manor meet a fatal end, and they offer a hefty price—fifty thousand dollars—for the job. Moriarty agrees, but imposes one critical condition: Balding must obey every order and let Moriarty control the outcome, a demand Balding accepts with quiet trepidation.
Meanwhile, Holmes is drawn back into detective work by a cryptic message from his informant, Porlock—a chain of letters, numbers, and the words “DOUGLAS” and “BIRLSTONE” that Whittaker’s Almanac helps him decode. The message portends trouble for John Douglas, and when Inspector Lestrade arrives to consult Holmes, the case begins to take shape. Holmes wagers Lestrade a bee-hive that Moriarty is somehow implicated, a playful nod to Holmes’s hobby of beekeeping, even as Watson urges caution. Against Watson’s counsel, Holmes and Lestrade travel to Birlstone to investigate the murder of Douglas.
At Birlstone, the investigators meet local Inspector Mason and scrutinize the murder scene. The weapon—a sawed-off shotgun—and the strange details surrounding Douglas’s body raise questions. Douglas’s wedding ring is missing, and the brand on his arm is identified as the mark of the Scowrers, a clue that ties the case to an American criminal society. The interviews with Douglas’s close circle—his friend Cecil Barker and his wife, Ettie Douglas—unfold in flashback-like recollections that echo passages from the original novel. Holmes challenges Ettie to tell the truth, while Lestrade remains convinced that the mystery is solved: Douglas, who had adopted the alias Birdy Edwards, was murdered by his old partner Balding, who had previously escaped from prison.
Yet Holmes is not swayed by straightforward explanations. He notices that a dumbbell is missing—a small but telling clue—and asks Watson to fetch his crook-handled umbrella, signaling a deeper plan afoot. He also hints at a hidden history of Birlstone through a well-worn book called the “History of Birlstone,” which foreshadows the priest-hole concealment that will soon come into play. In a tense moment, Mrs. Douglas reveals nothing definitive to Watson, and Barker’s presence beside her hints at a complex web of motive, jealousy, and deception.
As night falls, Holmes, Watson, Lestrade, and their quarry gather in the tower, where the truth of the crime will be laid bare. Moriarty and Moran join Balding on the scene, with the mastermind explaining that Balding should be found hidden near the crime site, ensuring that no one suspects his true identity. In a dramatic twist, the tower reveals a carefully staged series of events: Balding meets Douglas in the room, the two struggle over a knife, and the weapon fires—accidentally killing Balding in the melee. Barker and Mrs. Douglas enter, and Douglas explains a plan to Baldwin that would grant him a new life free from the Scowrers; he tries to transfer his own rings to Balding but cannot remove his wedding ring in the process. The pair dispose of Balding’s belongings by the moat, while Douglas congratulates Holmes on his deductions.
With the pieces aligned, Moriarty appears in a car with Moran and tries to confront Holmes in the priest-hole hideout. The confrontation escalates quickly, and when Moriarty ascends toward the tower’s ruined window, Holmes shoots him with a single, decisive shot. Moriarty plunges into the moat and drowns, the fall described by Watson as a “long drop.” Holmes, ever the composed detective, simply lights his pipe and notes that the drop was “a little longer than that required by law,” a cool finish to a case that has tested his wits to the limit.
The film’s conclusion emphasizes the triumph of Holmes’s intellect and moral clarity, even as the world’s most infamous mastermind meets an irredeemable end. Across the moody, shadow-filled rooms of Birlstone, the truth emerges not only about a single murder, but about loyalty, deception, and the difficult choices that define a life dedicated to justice. The retired detective, back in his element, proves that retirement was never truly an option for him—he remains a vigilant observer who can sift truth from illusion, even when the cost is steep and the shadows are long.
