In the sixth episode of "Young Sherlock," the story unfolds with Sherlock and James rushing back to Appleton Manor. Sherlock orders James to find Cordelia and take her to a safehouse while he confronts Silas. Instead, he finds his father waiting for him with a gun pointed at him.
Sherlock confronts Silas, accusing him of faking Beatrice's death to gain control of Cordelia's fortune. He questions him about the broken arm that Beatrice had when she supposedly drowned and brings up the mysterious doctor brought from Oxford. Silas claims that the doctor was Cordelia's idea, and Sherlock briefly believes him until Cordelia bursts into the room and confronts her husband.
Furious, Cordelia demands to know where Beatrice is. When she fires a warning shot, Silas uses the chaos to escape from Appleton Manor. Cordelia refuses to accept that her daughter is dead and insists on finding her if there is even the slightest chance she survived.
Meanwhile, in Oxford, Mycroft speaks with the doctor conducting an autopsy on Sir Hodge. The doctor notes that the body is unusually well preserved and concludes that Sir Hodge died by drowning. Confused, Mycroft asks Edie what Sir Hodge had been working on, but she admits she knows nothing about the project.
Soon after, Mycroft is summoned by the Foreign Secretary, who demands answers about the Chinese assassins, Professor Malik's disappearance, and Sir Hodge's death. Frustrated by the lack of information he has been given, Mycroft accuses the government of withholding details about Malik's research. Offended by the accusation, the Secretary dismisses him from his position.
Determined to continue the investigation, Mycroft visits Lestrade, who is equally frustrated by his inability to track down Shou'an or locate Professor Malik. Mycroft proposes they work together to uncover the truth, and Lestrade agrees.
Back at Appleton Manor, Sherlock, Cordelia, and James convened to review their knowledge of Silas and Beatrice's disappearance. They recalled that Nathan Burford, once employed by Silas, delivered animals he had hunted. As they examined Silas's ledger, they discovered a delivery scheduled for the day following Beatrice's supposed demise.
Guided by the address listed, the trio paid a visit to Mrs. Tilcott, who vividly recalled Nathan bringing her a young girl years ago. She assumed the child was an orphan and took her in. According to Mrs. Tilcott, the girl ran away at age 14, leaving behind only a short note.
Sherlock requested a tour of the girl's former room and discovered a chest brimming with framed butterfly specimens. Mrs. Tilcott explained that the girl received one every year on her birthday from an anonymous benefactor. Sherlock recognized the preservation method and realized it was unique to a particular taxidermist in London.
When they visited the shop, the taxidermist confirmed that he had been hired to send a framed butterfly to Beatrice each year. Meanwhile, Mycroft and Lestrade delved into police records connected to Professor Malik. Lestrade noticed that the files appeared to have been altered to protect him, but they managed to uncover a name and address linked to Malik.
Following this lead, they visited Alvie Gordon in Bayswater. Gordon revealed that Professor Malik had traveled to Paris. Unwilling to leave his wife alone, Lestrade asked Mycroft to continue the search himself. Mycroft thanked him and promised to share whatever he found.
As Sherlock, James, and Cordelia track down the individual funding the butterfly frames, Sherlock grows increasingly uneasy about the intimacy between James and his mother. He steps out of the taxi to caution James against flirting with her. When they finally arrive at the address linked to the deliveries, they discover it's one of Silas's safehouses. Inside, they find a photograph of an older Beatrice, confirming she survived her supposed demise. They also uncover Silas's travel records, which reveal his plans to be in Paris that weekend.
Before they can delve deeper, guards arrive and launch an attack. Sherlock and James rush Cordelia out of the house and release a herd of cows into the street to obstruct the officers and create chaos. Seizing this opportunity, the trio escapes and decides to travel to Paris to find both Silas and Beatrice.
Meanwhile, Shou'an and her companion Mei Yi continue their search for Professor Malik. Their investigation leads them to a man named Esad, who directs them to a coal mining facility. When they confront him, Esad attacks and stabs Mei Yi. Despite her injuries, she manages to steal an invitation from his pocket, revealing that Professor Malik will be in Paris. Before collapsing, she urges Shou'an to go there and avenge their family.
Sherlock, James, and Cordelia arrive in Paris during a period of civil unrest. Despite the turmoil, they make their way to Hotel Thérèse while searching for Beatrice. Speaking to a bellboy, they learn that Silas has been spotted at a nearby cabaret hall, Le Folies Bergère. When they go there, they unexpectedly encounter Mycroft, who explains that he is following Professor Malik. Sherlock reveals they are tracking Silas and that Beatrice may still be alive.
Inside the club, they soon spot Silas meeting with Professor Malik, Esad, and several government officials. Sherlock and James quietly follow the group while Cordelia creates a distraction. The men descend into a hidden chamber where Silas addresses a gathering. He introduces a deadly poison developed by Professor Malik that supposedly leaves no trace after use. To prove its effectiveness, Silas kills an insect sealed inside a glass jar.
The crowd remains skeptical, so Silas prepares to demonstrate the poison on a man. Before he can do so, Shou'an suddenly appears and shoots the jar containing the toxin. Panic spreads through the chamber as the men fear they have been exposed to the poison and rush toward the exits.
Silas attempts to flee in the chaos, but Sherlock calls out to him. As Shou'an raises her gun to shoot Silas, Sherlock steps between them and is shot as the episode ends.
