Millie Bobby Brown plays Enola Holmes, Sherlock Holmes’ much younger sister. She is also one of the producers, which allows her to let her character talk directly to the audience. She uses this technique to give the audience information.
The story starts on Enola’s 16th birthday, and her mother, Eudoria (Helena Bonham Carter), is missing. Enola searches for her mother using clues her mother hid among Enola’s gifts. Her older brothers, Mycroft (Sam Claflin) and Sherlock (Henry Cavill) show up. They haven’t seen Enola since she was young. Eudoria made Mycroft Enola’s guardian, and he enrolled Enola in boarding school. Enola uses money her mother left her and runs away.
Enola meets a boy, Viscount Tewkesbury (Louis Partridge), on the train and helps him escape Linthorn (Burn Gorman), who is trying to kill him. Enola and Tewkesbury escape Linthorn, reach London, and separate.
Enola uses disguises while searching for her mother and solving her other investigations. She uses the newspaper to try to contact her mother. Enola also encounters and overcomes Linthorn several more times. She decides to find Tewkesbury again and help him.
Mycroft asks Inspector Lestrade (Adeel Akhtar) to search for Enola. When Enola ends up back in the boarding school, Sherlock tells Enola he is impressed with her. Tewkesbury helps her escape. Enola and Tewkesbury discover his grandmother is trying to kill him to prevent him from taking his seat in the House of Lords and voting for a reform bill.
Sherlock takes Enola as his ward. When Enola returns to her room, Eudoria waits for her. Eudoria tells Enola why she left and must leave again. She adds she is proud of Enola and that Enola should send Eudoria a message if Enola ever needs her.
