In the BBC series Sherlock, what is the name of Sherlock Holmes’s secret sister?

Sherlock Holmes’s secret sister in the BBC television series Sherlock is named Eurus Holmes.

Eurus is introduced in the fourth series, whose second episode, “The Lying Detective,” reveals that John Watson’s therapist is actually Sherlock’s previously unknown sister in disguise. Her identity is confirmed in the series 4 finale, “The Final Problem,” which focuses on her imprisonment at the high-security facility Sherrinford and the psychological tests she forces Sherlock, Mycroft Holmes, and Watson to face.

Eurus is different from Enola Holmes, a character created for Nancy Springer’s later book series and not a member of Sherlock’s BBC television continuity. The name “Eurus” is drawn from Greek mythology, where Eurus is associated with the east wind. In the show, she is portrayed as exceptionally intelligent but emotionally isolated, and her childhood relationship with Sherlock helps explain the traumatic memory at the center of the finale.