In the fourth episode of "Young Sherlock," the story unfolds with Sherlock rushing to the mental health facility where his mother, Cordelia, is being held. He questions his mother about whether she's been speaking with anyone, and discovers that there are secret listeners monitoring her. He breaks into a wall and discovers a hidden listening device. As the doctors and guards rush into the room, Sherlock stealthily escorts his mother out of the facility. Cordelia saves Sherlock from a nurse's attack by delivering an electric shock, and the two escape together.
Meanwhile, Sir Hodge threatens to hang Shou'an for her involvement in the murders of the professors. He's about to order the executioner to carry out the sentence when Mycroft steps in to stop him. Mycroft insists that they need Shou'an alive because she's their only connection to the person behind these murders.
The next morning, James arrives at the Holmes family house in Appleton Manor and is surprised by the collection of items there. Sherlock eventually arrives and is reminded of his childhood when he was sent to boarding school.
Sherlock introduces his mother to James, and James realizes that Cordelia is grieving for her deceased daughter, Beatrice. Despite trying to ignore the fact that Cordelia isn't doing well, James insists on informing Mr. Holmes and asking him to return home. When Cordelia runs out looking for Beatrice in the lake, Sherlock asks their steward, Mr. Crowle, to call for their village physician, Dr. Maltby. Meanwhile, the director of the mental asylum orders the guard to search for Cordelia after she escapes. Dr. Maltby checks on Cordelia while this is happening and gives her medication to help her relax.
In private, James and Sherlock try to determine the meaning of the phrase "bird's claw," as it was the last thing Shou'an told him before her arrest. Sherlock suddenly realizes that "bird's claw" likely refers to the cane Professor Malik uses, as its handle is claw-shaped. He instructs Mrs. Crowle to take care of his mother and gives strict instructions for Crowle to deny anyone entry into their house.
Sherlock and James return to Oxford to visit Mycroft, their brother-in-law, to discuss Professor Malik and his cane. They imply that their mother had seen the man in the asylum, but Mycroft remains skeptical.
James and Sherlock ponder the mystery of Professor Malik's disappearance, given that Shou'an is already in custody. Sherlock requests a meeting with Shou'an and learns that she witnessed Professor Malik listening to recordings of Cordelia's conversations with her doctors at a safe house.
Sherlock informs Sir Hodge that Professor Malik was not present when Shou'an planted the bomb, suggesting that the professor was betraying him. He convinces Sir Hodge to release Shou'an from prison, allowing them to follow her to the safe house. There, they discover the real Princess Shou'an, who has been kidnapped. Sir Hodge apologizes to the real princess and learns that Professor Malik had already moved to a different hideout.
At the same time, the fake Shou'an leads Sherlock to the room where she saw Professor Malik listening to the recordings. Inside, Sherlock and James find tapes of all the treatment sessions conducted on Cordelia at the mental asylum. Sherlock is horrified when one of the recordings ends with Cordelia screaming and crying for help after being subjected to shock therapy.
Sherlock and James discover a transcript of all the conversations Cordelia had with her visitors, including a meeting with a lawyer named Lawson Jaggers. They learn that the recording of this conversation was tampered with, indicating that someone was trying to keep a secret involving Cordelia. Sherlock informs Mycroft about this and asks him to search for Professor Malik.
Meanwhile, the fake Shou'an takes advantage of the chaos and escapes police custody. Just as a cop is about to capture her, her friend kills the cop to rescue her.
Mycroft, Sir Hodge, Edie, and the constables embark on a quest to uncover Professor Malik's new hiding spot, guided by the cryptic clues provided by the genuine Princess Shou'an. Meanwhile, Sherlock and James stealthily infiltrate Mr. Jaggers' residence, where they encounter his lifeless body. James' keen eye catches the signs of a struggle on Mr. Jaggers' hands, leading him to deduce that the man was brutally killed and then hanged. As they proceed to inform the police of this murder, the constable hands Sherlock a wire from Mr. Crowle.
In a rush, Sherlock returns home to prevent his mother from being kidnapped by the mental asylum staff. Mrs. Crowle brandishes a gun at the director of the asylum, forcing him to retreat, leaving Cordelia alone and vulnerable.
Sir Hodge and Edie arrive at Abdon Abbey, where they discover Professor Malik in hiding. Sir Hodge confronts the professor, threatening to shoot him for betraying him. Malik claims that he never intended for Sir Hodge to take credit for his accomplishments. In a fit of rage, Sir Hodge is about to execute Professor Malik when the latter drugs and kills him.
The episode concludes with the constables stumbling upon Sir Hodge's lifeless body as Mr. Silas Holmes finally returns to Appleton Manor.
