3. The Final Problem

Complete story — includes the ending

Sherlock and Watson – who were shot with a tranquilliser 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 skeptical at the suggestion that she escaped, the trio discover that Eurus compromised the staff and controls the entire asylum. She subjects the trio to various 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 the love and relationship with a brother that she never had, and Eurus stands down. Sherlock and Watson return to their apartment, and find another message from Mary imploring them to stay together. The two rebuild the flat to its original form before meeting various unusual clients. The title matches the Doyle short story " The Final Problem ", but the plot contains elements from the short stories " The Adventure of the Musgrave Ritual ", " The Adventure of the Three Garridebs ", and " The Adventure of the Gloria Scott ".