In the opening scene of Episode 3 of Young Sherlock, we are transported to the Gansu Corridor in China, six months prior to the present day. The story unfolds as Shou'an returns home to find her family brutally murdered. Running to her cottage, she witnesses the tragic scene where her parents and other elders of her community are laid to rest. Together with the other women, she takes care of the deceased.
The episode then shifts to the present, where Shou'an waits anxiously outside Professor Enright's house. Sherlock and James are trying to hide from the local crowd, who are unaware of their mission. A man steps in to distract the cops, allowing James and Sherlock to enter the premises. They begin searching for clues that could explain Shou'an's motive for killing the professors.
James discovers a paper that Professor Enright was writing about mineral extraction in the Gansu Corridor. He points out that Sir Hodge made a fortune from mining gold at the same location. As they discover a clue to Professor Enright's hiding place, the cops return to the apartment. They try to arrest both Sherlock and James, but the two manage to flee just in time.
Meanwhile, Mycroft is spying on a conversation between Sir Hodge and the Foreign Secretary. He discovers that Sir Hodge was working on a special project with the four professors, two of whom were murdered. Sir Hodge assures the Foreign Secretary that Professor Malik is in safe custody while Professor Enright is hiding. When Sir Hodge learns that Mycroft has been spying on his conversation, he confronts him about it. Mycroft tries to defend himself, suggesting that he is only trying to save his family. Sir Hodge fires Mycroft as a punishment for getting in his way.
This episode of Young Sherlock takes us through a gripping tale of murder, mystery, and intrigue, as we follow the characters on their quest to uncover the truth behind Shou'an's actions and the mysterious project being conducted by the professors.
In the following exchange between James and Prudence Hamilton, a natural sciences scholar and Professor Enright's student, Sherlock decodes their conversation to deduce that Professor Enright was hiding in the bell towers. Recalling the numerous glasses at Enright's residence, Sherlock deduces the precise location of the bell tower where the professor was concealed. They rush to the tower in an attempt to save Enright from a certain death, but arrive too late to intervene. Just as they arrive, Shou'an pushes Professor Enright from the tower. Sherlock attempts to halt her escape, inquiring how she discovered Enright's hiding place. Shou'an reveals that it was James and herself who had assisted her in locating the professor's location.
That night, Sherlock blames himself for Professor Enright's demise, but James helps him see that their actions were not responsible for Shou'an's actions. Constable Lestrade informs Sir Hodge of Professor Enright's death, and the Foreign Secretary informs Sir Hodge of his visit to Oxford, causing the latter to become concerned.
Sherlock and James examine Shou'an's glove, which was left in the former's hand the previous night. They return to the store and learn that the glove was purchased two weeks earlier. Sherlock tells James that he recalls transporting Shou'an's luggage to her lodge and is convinced that something is amiss.
At the same time, Shou'an's associate informs her that she should return to China as he will take care of Professor Malik in his own way. Shou'an insists on avenging the murder of her family, suggesting that Malik was the mastermind behind their deaths. However, the man urges Shou'an to follow his instructions and leaves. At this point, Shou'an realizes that she has been manipulated from the beginning.
Sherlock and James meet Mycroft to inform him about Shou'an and the murders she had been committing. Mycroft escorts them to speak with Ezra Hornsby, the man who had escorted Shou'an to Oxford. Ezra shares his account of the attack and how Shou'an had disappeared for ten minutes when the thieves kidnapped her and stole the scrolls. The thieves also killed Shou'an's escort before taking her hostage.
Sherlock concludes that the person posing as Shou'an is not the real princess, as Ezra's spectacles were broken, and the only man who had truly seen the real Shou'an was dead. A flashback reveals a distraught Shou'an in China after her family's murder. Her associate, Esad Kasgarli, convinces her to kill the four apostles to avenge her family's death.
Meanwhile, Shou'an asks her friend to come from London to Oxford and inform him about Esad's betrayal. At the same time, Mycroft tries to alert Sir Hodge about Shou'an, but he refuses to listen. Mycroft forcefully interrupts Sir Hodge's meeting with the Foreign Minister and informs him about the fake Shou'an and her involvement in the murders. The Foreign Minister praises Mycroft for his wit, but Mycroft credits Sherlock. Sherlock and James reveal their plan to trap the fake Shou'an by using Professor Malik as bait to lure her in.
That night, Detective Fitget and the constables are on watch, waiting for Shou'an to attack, while Sir Hodge, Mycroft, Sherlock, and James sit patiently in the room with Professor Malik. Sir Hodge threatens to fire Mycroft if Shou'an does not show up. Mycroft warns Sherlock that he would be sent to prison if he is fired.
A flashback shows how Shou'an had snuck into Professor Malik's house earlier that day while her friend caused a distraction outside. With the cops distracted, Shou'an emerges from the box to kill Professor Malik but is surprised to see Sherlock waiting for her.
Sherlock threatens to shoot Shou'an and asks what she is after. Shou'an says something to Sherlock that makes him worried for his mother's safety. Sherlock tries to stop her but is unsuccessful as she is arrested. James celebrates their victory, but Sherlock is still shell-shocked by this sudden turn of events.
