Two years after his apparent death in The Reichenbach Fall, Sherlock Holmes Benedict Cumberbatch has been fully exonerated from the slander spread by Moriarty Andrew Scott and secretly returns to London after Mycroft Holmes Mark Gatiss corners him in Siberia, where he’s been quietly dismantling Moriarty’s network. Holmes is recruited by his brother to help uncover an imminent, massive terrorist attack orchestrated against the city, a challenge that tests loyalty, trust, and the limits of what two longtime colleagues can endure.
An interwoven sequence sketches a version of how Holmes might have faked his own death: leaping from a rooftop with a bungee cord, rebounding, and slipping back into a building through a window. While Holmes was away, a shadowy network of homeless allies stage a deception—masking Moriarty to resemble Holmes, dragging him onto the street, and dousing him with fake blood. Moriarty’s body is left on the pavement wearing a Sherlock mask to mislead John Watson Martin Freeman and other bystanders. Meanwhile, Watson lies blinded on the ground, having been knocked over by a cyclist who was part of the ruse, and is hypnotized by Derren Brown Derren Brown to time the setup precisely. This troubling tableau is later revealed to be a conspiracy theory imagined by Philip Anderson Jonathan Aris, who feels guilty about Sherlock’s supposed death and even founded a club called the Empty Hearse to discuss such theories.
Back in the present, Watson has a girlfriend, Mary Morstan Amanda Abbington, and plans to propose in a restaurant. Disguised as a French waiter, Holmes approaches the couple, but Watson does not recognize him. When Sherlock reveals his true identity, Watson attacks him in three different restaurants. Sherlock explains that the “death” was a fraud, a revelation that wounds because many people—including Molly Hooper Louise Brealey—knew of the plan but kept it from John. With Watson's resistance clear, Sherlock enlists Molly to assist with the next case; since John refuses to cooperate fully, Holmes must rely on Molly’s expertise while hoping to recruit an assistant for a high-stakes investigation.
Mary then receives a coded message in a skip code (first and every three words) indicating John’s kidnapping and a danger to his life unless rescued, with a hint to the location. Sherlock and Mary race to intervene, riding a motorcycle to pull John from a bonfire where a Guy Fawkes effigy is about to be burned—a dramatic rescue that underlines how far Holmes will go to protect his friend. The rescue marks a turning point, reigniting the partnership between Holmes and Watson as they confront Mycroft’s terrorist plot with renewed urgency.
During the investigation, Sherlock is shown a video by a London Underground worker showing a passenger vanishing from a train near Parliament. The missing passenger is identified as a foreign agent within the House of Lords, and Sherlock deduces that the attack will strike Parliament during a late-night hearing on a new anti-terrorism bill on Guy Fawkes Night. The team discovers an abandoned Underground station where a carriage is diverted and rigged with explosives. Sherlock manages to defuse the device by hitting the off-switch, but the tense moment leaves John fearing the bomb could have been unstoppable, prompting a heartfelt apology from Sherlock for drawing him into danger and underscoring how much John has come to mean to him. Sherlock and Mycroft had anticipated thirteen possible outcomes, and the whole sequence leaves Moriarty’s supposed death exposed as part of a larger scheme to erode Moriarty’s network.
In a climactic turn, Sherlock reveals to Anderson how the faked-death ruse was orchestrated to undermine Moriarty’s influence, using the homeless network, a decoy body double, and a meticulously timed sequence that convinced many observers. An alternate version of the faked death is shown, leaving the truth tantalizingly ambiguous. The culmination sees Moran arrested as the plan comes together, with a final shot of a bespectacled man with blue eyes watching the rescue of John and Mary unfold. John remains unsure exactly how Holmes survived the rooftop leap or why anyone would want to burn him in a bonfire, but the evidence points to a calculated, cleverly executed gambit designed to cripple Moriarty once and for all.
