The fifth episode of "Young Sherlock" opens with a flashback, revealing a youthful Sherlock, Beatrice, and Mycroft playing by the river. Suddenly, Beatrice vanishes, and the villagers search tirelessly through the night until they find her drowned body in the river.
In the present, Silas Holmes, Sherlock's father, arrives at Appleton Manor. He greets Sherlock and Cordelia, learning that Sherlock has freed his mother from the mental asylum. Silas is understandably upset and tries to confront his son, but Cordelia interjects, insisting that the family sit down for dinner.
At the dinner table, Silas announces that he has completed his travels and plans to stay at Appleton Manor to care for Cordelia. He speaks enthusiastically about his expeditions and recent scientific developments, prompting James to raise a toast.
As the adults converse, Sherlock is preoccupied. Cordelia mentions Mycroft and soon begins thinking about Beatrice. Sensing her distress, Silas starts singing and encourages everyone to join him in a dance to lighten the mood.
Later that night, Sherlock confides in his father everything that happened in Oxford, including the events surrounding Professor Malik. When he steps out to fetch more alcohol, he notices that a button is missing from Silas's coat. This makes Sherlock wonder if his father was somehow involved in Mr Jaggers' murder.
James tries to discuss the case with Sherlock, but Sherlock remains distracted by visions of his sister. He eventually goes to bed but wakes from a nightmare of his mother crying while Beatrice drowns in the river.
The next morning, Silas tells Sherlock that James has taken the horse and gone out early. Silas himself plans to visit the mental asylum but refuses to let Sherlock accompany him.
Meanwhile, James questions one of Mr Jaggers' clients, Mrs Turner, before returning to Appleton Manor. He shares his findings with Sherlock, explaining that Cordelia originally came from a wealthy family. However, most of that fortune was transferred to Silas after their marriage.
With the recent Property Act granting married women enhanced financial autonomy, Mr. Jaggers approached Cordelia to reclaim control of her inheritance, thereby enabling her to achieve financial independence. James believes that Silas orchestrated the secret recording of Cordelia's conversations by the asylum director and subsequently arranged for Mr. Jaggers' murder to prevent him from aiding her. Sherlock vehemently rejects this accusation, leading the discussion to escalate into a heated argument. Personal insults fly between the two men until Sherlock angrily expels James from the house.
Shortly thereafter, Silas returns and informs Sherlock of Professor Malik's experiments involving the Holmes family. He also requests a statement from Sherlock for the police. Still uncertain about his trust in his father, Sherlock later seeks out James and apologizes for their earlier disagreement. The two return to Appleton Manor together.
Sherlock stealthily enters Silas's study and steals the key to his safe, handing it over to James. As Silas unexpectedly appears, Sherlock diverts his attention while James searches the safe for financial records. Sherlock casually inquires whether Silas has sent a telegram inviting Mycroft to join the family reunion. As Silas heads towards his study, James slips out unnoticed.
Later, James reveals what he has discovered. Silas had several failed businesses until the year preceding Beatrice's death. Cordelia's father had left a substantial inheritance to his grandchildren, Mycroft, Sherlock, and Beatrice, which Cordelia managed herself.
After Beatrice's untimely demise, Cordelia began to experience neurological issues that eventually necessitated her institutionalization. According to James, this opened the door for Silas to take control of the family's fortune. He harbors a suspicion that Silas might have played a role in Beatrice's death.
Shaken by this accusation, Sherlock spoke with Cordelia about the day Beatrice passed away. He confesses that he has always felt responsible for leaving his sister alone that fateful afternoon. Cordelia urges him to cease blaming himself, reminding him of the conversation she had with Sherlock before Beatrice went to confront Silas.
Realizing that Silas could have been the last person to see Beatrice alive, Sherlock and James set out to find Nathan Burford, the man who discovered Beatrice's body. Nathan's daughter informs them that her father has since passed away, but she recalls playing with the Holmes children as a child and that Silas had been kind to her family, even forgiving all of Nathan's debts after Beatrice's death.
Despite these facts, Sherlock insists that they still need concrete evidence. The duo visit Dr. Maltby, the family physician, to inquire about Beatrice's demise. Dr. Maltby reveals that he was never called upon to perform an autopsy; instead, another doctor from Oxford was reportedly brought in.
The revelation unsettles Sherlock. Upon returning home, he confronts Silas, asking if he derives pleasure from watching butterflies die for his experiments. Sherlock then turns to Cordelia and asks her to recall what happened when Nathan brought Beatrice's body home. Cordelia remembers rushing toward her daughter as Silas lifted the body and Nathan tried to restrain her.
From this recollection, Sherlock realizes that Nathan had been preventing Cordelia from seeing the body clearly. In fact, she never truly saw Beatrice's face after she was found. At that juncture, Silas enters with Cordelia's medication. Sherlock takes one of the tablets and notices that it looks different from the medicine Dr. Maltby had given her just days earlier.
Determined to uncover the truth, Sherlock ventures out that night and exhumes Beatrice's grave. Back at the house, Cordelia enquires about the night their daughter died from Silas, explaining that Sherlock has been asking probing questions. Silas becomes uneasy and goes searching for his son. When he enters Sherlock's room, he finds notes scattered everywhere. Looking out the window, he spots Sherlock digging in the graveyard.
The episode concludes with Sherlock informing James that the skeleton in the grave cannot be Beatrice's, as she had a broken arm before her alleged death.
