A man named Bentley Bobster walks down a street in London, England, followed by a cloaked figure, who shoots him in the neck with a blow-dart. Moments later, Bobster enters a restaurant, orders turkey, and suffers violent hallucinations of the bird coming to life and attacking him. The other guests watch as he fights the imaginary predator. Bobster races home and locks himself in his room, where his hallucinations continue. The room appears to catch fire, and he leaps through a window to his death. Elsewhere, young John Watson begins life at a new school named Brompton Academy. When he meets a student named Sherlock Holmes, the two become instant friends. Sherlock impresses John with his skills of deduction, and John asks how to hone the skills himself. Sherlock introduces John to his girl friend, Elizabeth, and her uncle, Rupert T. Waxflatter, the retired headmaster of the school, who is also Sherlock’s mentor. Waxflatter continues to live on campus in an attic with Elizabeth, where he conducts scientific experiments. Waxflatter is visited by an unknown man, and he excuses himself from Elizabeth and her friends to meet with him. Sherlock’s suspicions are aroused when he sees a newspaper article about Bobster’s suicide that Waxflatter has circled. Sometime later, the cloaked figure visits a church and shoots a blow-dart into the neck of Reverend Duncan Nesbitt. The minister flees into the street to escape from an imagined attacker, and is run over and killed by a passing carriage. At Brompton, Sherlock’s classmate, Dudley, puts the young detective’s investigative skills to a test by hiding a trophy and giving him one hour to find it. Using deductive reasoning, Sherlock successfully finds the trophy. When Sherlock sees a news article about the death of the Reverend Nesbitt, he visits police headquarters, where he is a familiar face, and tells policeman Lestrade his beliefs that the two deaths were murders, not suicides. However, Lestrade dismisses him. Later, Sherlock gets expelled after Dudley makes it appear he cheated on an exam. Despite appealing to his favorite professor, Rathe, Sherlock is banished from campus. Before leaving school, Sherlock gets revenge by secretly bleaching Dudley’s hair. Elsewhere, as Waxflatter enters an antiques shop, the cloaked man shoots him with a dart. Waxflatter soon envisions statues of bats coming to life and attacking him, and jabs at them with a knife, inadvertently stabbing himself in the chest. As Sherlock bids farewell to John Watson, they hear police alarms and race to the scene of the commotion. The cloaked figure rushes past, dropping his blow-dart, and John picks it up. Sherlock arrives at Waxflatter’s side as he speaks his dying words. At the funeral, Sherlock chases the man he saw visit Waxflatter, but the man gets away. Sometime later, Sherlock sneaks into Elizabeth’s room and asks her about the unknown man. He decides to secretly live with Elizabeth on campus and investigate his mentor’s death, asking for John’s help. The young men take the blow-pipe to a curio shop and ask the proprietor about the object. He tells them it is an Egyptian artifact, and directs them to a tavern owner who bought a similar item. When Sherlock and John show the man the blow-pipe, he points a gun at them, and orders them to leave. They visit the school library and read about Egyptian cultural history, discovering that the blow-pipe was historically used by a religious sect to shoot poisoned thorns, which cause terrifying hallucinations. Elizabeth reveals that her dog chased after a cloaked man, and gives Sherlock a piece of cloth that the dog tore from the escaping villain. Examining the cloth leads them to a warehouse where they discover a pyramid within. Walking inside the pyramid, they discover a temple, in which a secret ceremony is underway. A young girl is wrapped like a mummy, and Sherlock stops the members from pouring hot wax and “mummifying” the living girl. The angry worshippers chase after the friends, shooting blow-darts at them. While Sherlock, John, and Elizabeth hide in a cemetery, the hallucinations take effect on all of them. A worshipper tries to kill Sherlock, but he is rescued by the cemetery caretaker who shoots a gun at the attacker. The friends revive, and go to police headquarters, where Sherlock tells Lestrade of their ordeal. However, Lestrade, threatened by Sherlock’s expertise, refuses to believe his theories. Sherlock leaves behind the poisoned thorns for Lestrade to analyze, and Lestrade later pricks his finger on one of them. Meanwhile, in Waxflatter’s home, John discovers a portrait of Waxflatter and a group of men, and Sherlock recognizes them as the murder victims, identifying the unknown visitor as Chester Cragwitch. Before he can continue his investigation, Sherlock is discovered on campus by Professor Rathe, who orders that he and John leave the school the following day. Rathe locks the boys in a room for the night, but they sneak out and visit Mr. Cragwitch, who fires a warning shot at the intruders. Sherlock introduces himself, and Cragwitch invites them inside, and shares his history with the men in the portrait. He explains that they were business partners who planned to build a luxury hotel in Egypt. During construction, they discovered an underground pyramid housing the tombs of five Egyptian princesses, and several artifacts. When they prepared to send the artifacts back to England, the villagers revolted, claiming desecration, and threatened their lives. English forces arrived to protect the businessmen, and in the resulting riots, several villages were burned to the ground. As Cragwitch shares the story, the cloaked man, who hides within his home, shoots him with a blow-dart. Cragwitch begins to hallucinate, and Sherlock helps keep him sane during the episode. When he recovers, he continues the story of how, a year after the incident, he and his business partners received a letter from a boy and his sister whose parents were killed in the fires, and vowed that an ancient order of Egyptians would take revenge, and replace the bodies of the five princesses. The boy’s name, “Eh-tar,” was the last word spoken by Waxflatter. The poison again takes hold of Cragwitch, and he attacks Sherlock. Lestrade arrives, knocking Cragwitch unconscious. He tells Sherlock that he finally believes his story after being pricked by the poison thorn and suffering hallucinations himself, and his investigation has led him to Cragwitch. Elsewhere, Elizabeth is attacked by the school nurse, Mrs. Dribb, whom she realizes is the blow-dart attacker. Professor Rathe enters, and Elizabeth begs at his feet, but quickly realizes he is working with Mrs. Dribb. Rathe hypnotizes Elizabeth, planning to use her as the “fifth princess” to be sacrificed. Elsewhere, Sherlock realizes that Rathe is the villain, and races to find him. He sees Rathe leave in a carriage, and follows him to the temple. The ceremony begins, and Elizabeth is wrapped in gauze. With hundreds of followers in attendance, Sherlock struggles to find a way to rescue his love. Before Elizabeth is entombed in hot wax, Sherlock swings down from the rafters, and sets the temple ablaze. He fights several attackers while John flees with Elizabeth. Sherlock fights Mrs. Dribb, whom he realizes is Rathe’s sister and the group’s most lethal member, and he blows the poisonous dart back into her own throat before she can shoot him. Rathe punches John, and reclaims Elizabeth. However, as Rathe drives away with her in his carriage, John rigs a chain to the buggy, stopping his escape, and rescuing Sherlock from the burning temple at the same time. Sherlock rushes to Elizabeth’s side, and she awakens from her spell. As the friends leave, Rathe reappears and fires a gun at Sherlock, but Elizabeth jumps in the line of fire and is hit. When she collapses, Sherlock challenges Rathe to a duel. As they engage in a sword fight, Rathe falls through a frozen river and disappears. As Elizabeth dies, Sherlock promises that they will be reunited one day. In time, Lestrade takes credit for solving the murders, and Sherlock and John return to school. Sherlock tells John how he came to realize that Rathe was the culprit. When John reveals his epiphany that “Rathe” is “Eh-tar” spelled backwards, Sherlock is impressed with his friend. Sherlock bids farewell to John, explaining that the memories at Brompton would haunt him, and vows to spend the rest of his life alone.