„Sherlock is asked to investigate the mysterious death of a young man, which he solves quickly but he is led into another mystery when a bust of Margaret Thatcher owned by the dead man’s father is smashed. Further busts are smashed and Sherlock discovers that the mystery is linked to Mary and her past as a government agent. A figure from her past is bent on revenge in the belief that Mary betrayed him, but it is discovered that the traitor was the secretary of a British Parliamentary member. Mary is killed by the secretary when jumping in front of a bullet meant for Sherlock. John blames Sherlock for Mary’s death, and their relationship is fractured.
Sherlock is contacted by the daughter of entrepreneur Culverton Smith, who she claims has confessed to a murder but she does not know who the victim was as her father has used a drug on her that inhibits memory. Sherlock deduces that her father is a serial killer and sets out to expose him, but he has returned to narcotics use since Mary’s death and unable to clearly distinguish his own thoughts from reality. He confronts and attacks Smith, and John is forced to subdue him. While recovering in the hospital, Smith appears in Sherlock’s room, confesses and then tries to kill him. John bursts in just in time to save Sherlock, who reveals that his behavior up to that point was not just an elaborate ploy to expose Smith, but also fulfilling Mary’s last wish for him to „Save John“. Later John’s therapist reveals that she is actually Sherlock’s secret sister, Eurus, and has been using disguises to manipulate both Sherlock and Watson. The episode ends with Eurus firing a shot at John.
Sherlock and Watson – who had been shot with a tranquilizer by Eurus – trick Mycroft into acknowledging her existence. Eurus steps up her attacks on Sherlock, culminating in the bombing of his Baker Street apartment. Sherlock, Watson and Mycroft venture forth to Sherrinford, a maximum-security psychiatric facility where Eurus is housed. Although Mycroft is sceptical at the suggestion that she has escaped, the trio discover that Eurus has compromised the staff and controls the entire Sherrinford asylum. She subjects the trio to a series of ordeals, testing their morals by forcing them to choose which of her victims live and die and ultimately forcing Sherlock to confront the memory of „Redbeard“, a childhood friend whose death set in motion events that saw Eurus incarcerated. Realising that she will continue to test him until someone he cares for dies, Sherlock tries to connect with her on an emotional level, offering her the love and relationship with a brother that she never had, and Eurus stands down. Sherlock and Watson return to the Baker Street apartment, where they find another message from Mary imploring them to stay together. A time lapse montage shows them rebuilding the Baker Street flat to its original lived in form before meeting a series of unusual clients.“ (Quelle)
3x90min. An einem Abend. Mit der reizenden Kollegin MR. Zwischendrin Pizza. Und Chips. Ihr seht schon. Ein wilder Abend. Voller kcal. Und Rätsel. Buchstäblich und sprichwörtlich. Es gibt vieles, was mich stört. Es gibt allerdings auch vieles, was mich packt und rührt. Von Hund und Frau. Und Opfer. Und Liebesschwüre unter Hochdruck. Und irgendwie hoffe ich, dass es doch noch weitergeht, doch noch eine fünfte Staffel geben wird.