Season synopsis
Contains spoilers for this season and earlier seasons.
Moriarty abandons the swimming-pool confrontation after receiving a phone call, leaving Sherlock and John alive. Their next major case brings them to Irene Adler, whose phone contains compromising royal photographs and intelligence that powerful people want suppressed. Sherlock decodes flight information for her, inadvertently exposing Mycroft’s counterterrorism operation to Moriarty. Irene tries to trade her remaining secrets for protection, but Sherlock works out her phone password and removes her bargaining power. Although Mycroft later believes she has been executed, Sherlock secretly saves her. John’s accounts of their cases, meanwhile, have helped make his friend famous.
On Dartmoor, Henry Knight asks them to investigate the enormous hound he remembers killing his father. Their search reaches the Baskerville military laboratory, where even Sherlock becomes frightened by what he sees. The creature’s monstrous appearance comes from a hallucinogenic chemical rather than a supernatural animal. Dr Frankland murdered Henry’s father and has been dosing Henry to conceal the crime. Confronted in the hollow, Frankland runs into the base’s minefield and dies; the investigators can finally separate Henry’s memories from the terror imposed on him.
Moriarty turns Sherlock’s celebrity against him, threatening a jury into acquitting him and manufacturing evidence that the detective stages his own cases. He even poses as an actor hired to play Sherlock’s criminal enemy. On the roof of St Bartholomew’s Hospital, Moriarty says assassins will kill John, Mrs Hudson and Lestrade unless Sherlock jumps. Moriarty shoots himself to prevent Sherlock forcing him to cancel the order. Sherlock calls John and plunges from the roof. John mourns him, but the final scene shows Sherlock watching from a distance, alive; how he survived remains unexplained.