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As an adult, Eurus adopted the alias Elizabeth and began a flirtatious relationship with John Watson after meeting him on a bus. Disguising herself as the daughter of Culverton Smith, Eurus met up with her brother Sherlock.
She later became John's new therapist with yet another disguise. During a therapy session with John, she revealed herself to be Sherlock's sister before shooting a tranquilizer dart in the direction of John.
Eurus is the youngest child, being 1 year younger than Sherlock, and 8 years younger than Mycroft (Mycroft says that there was 7 year age gap between him and Sherlock and 1 year age gap between Sherlock and Eurus which results in the order - Mycroft, then Sherlock, then Eurus). Sherlock had forgotten he had a sister for a long time, after she drowned his childhood best friend, Victor, out of jealousy. The traumatized toddler Sherlock had then slowly erased her memory, and fabricated a different reality where Victor had been a dog named Redbeard who had been put down.
Eurus is more clever than either siblings, but lacks sanity, and cannot tell the difference between laughing and screaming, as she implies when talking to Sherlock in 'The Final Problem', referencing when she 'made him laugh all night', before realizing he had been screaming when their parents confronted. She also taught Sherlock how to play the violin.
Mycroft once says that she does not talk to people, but, rather, 'reprograms' them. This is evident when she talks her warden into allowing her to take control, and she runs the prison instead of him.
Eurus was sent away when she was a young child, after burning their house down. She also burned down the place she was being kept in, and then confined in a prison on the island of Sherrinford under the advisement of Mycroft, who is terrified of her. Mycroft utilized her incredible mental prowess several times to predict terrorist attacks, however, in exchange for 'treats'. One of the 'treats' was a violin, while a different on was 5 minutes of unsupervised conversation with James Moriarty. During this conversation, they made several arrangements for a torturous trap for John, Sherlock, and Mycroft.
She saw herself (every time she closed her eyes) as a little girl, trapped on a plane about to crash, while all the passengers are asleep. At the end of 'The Final Problem', after her strange puzzle was beaten and Sherlock comforted her, she was returned to Sherrinford, but refused to speak- however, she and Sherlock play duets on the violin together.
Eurus Holmes appeared in the Sherlock episodes:
Behind the scenes Edit
Eurus Holmes is played by Sian Brooke