Enola Holmes, portrayed by Millie Bobby Brown, is the youngest member of the illustrious Holmes family. With her exceptional intellect, keen observational skills, and profound insight, she boldly challenges the societal expectations imposed on women of her time. Under the guidance of her mother, Eudoria, played by Helena Bonham Carter, Enola has learned a variety of skills, ranging from chess to jujitsu, with a strong emphasis on becoming a fiercely independent thinker.
On her sixteenth birthday, Enola awakens to a shocking reality; her mother has vanished without a trace, leaving behind only a few birthday gifts. A week later, she heads to the train station to reunite with her brothers, Mycroft, played by Sam Claflin, and Sherlock, depicted by Henry Cavill. They hardly recognize her due to the years that have passed. While Sherlock sees Enola's potential intellect, Mycroft views her as a burden. Determined to be her legal guardian, Mycroft intends to send her off to a strict finishing school run by the unyielding Miss Harrison, portrayed by Fiona Shaw. Infuriated by the prospect of being sent away, Enola is further disheartened to discover that her mother had been increasing her living expenses to bilk Mycroft for more money.
Enola soon uncovers that the flower cards left by her mother contain hidden messages directing her to concealed funds, which she cleverly utilizes to escape by disguising herself as a boy. On the train, she unexpectedly encounters Tewkesbury, portrayed by Louis Partridge, the young Viscount, who is hiding in a travel bag. Mistakenly thinking he lacks wits, she warns him about a man in a brown bowler hat, namely Linthorn, played by Burn Gorman, who is hunting him down. In a thrilling moment of danger, they leap from the train after Linthorn makes an attempt on Tewkesbury's life.
With no food in their possession, the two must forage for sustenance as they travel to London, eventually parting ways. Enola, now disguised as a Victorian lady to evade Mycroft's search efforts, continues her quest to find her mother. She leaves coded messages in personal newspaper advertisements and visits an address frequently mentioned in Eudoria's letters. There, she meets Edith, portrayed by Susan Wokoma, who operates a self-defense class for women. While Edith recognizes Enola, she refuses to reveal anything about her mother, leading Enola to uncover pamphlets in Edith's office that indicate her mother's involvement with a radical group of suffragettes advocating for women's voting rights.
As Enola delves deeper into her search, she faces threats from Linthorn, who goes to horrific lengths to extract information from her about Tewkesbury, even attempting to drown her. Thankfully, she manages to ignite explosives to escape his clutches. Shifting her focus from finding her mother to rescuing Tewkesbury, Enola visits his family estate, Basilwether Hall, where she meets Sir Whimbrel, played by David Bamber, as well as Tewkesbury's mother, Lady Tewkesbury, and grandmother, played by Hattie Morahan and Frances De La Tour, respectively. Trusting Enola proves a challenge for them, leading her to adopt the guise of Sherlock's assistant to gain their confidence.
Meanwhile, Mycroft enlists the help of Inspector Lestrade, played by Adeel Akhtar, from Scotland Yard to search for Enola. While investigating the estate grounds, Enola discovers Tewkesbury’s tree-house and follows a series of deceptive clues to find him selling flowers in Covent Garden. She warns him of impending danger, and in the ensuing chaos, she gets captured by Lestrade and taken back to Miss Harrison's school. However, when Sherlock pays her a visit, he admits to being impressed by her detective skills.
In a daring turn, Tewkesbury sneaks into the school, and they make their escape using Miss Harrison's motor car. Faced with a decision at a fork in the road, Enola opts not to return to London but instead to confront Tewkesbury's uncle in a bid to protect him, fully aware that the uncle has plotted his demise to seize the family estate. Upon reaching the estate, they find it eerily deserted, only to be confronted by Linthorn, who attacks them with a shotgun. Utilizing her jujitsu skills, Enola trips him, resulting in a fatal injury. The plot thickens when Tewkesbury's grandmother emerges as the true villain, opposed to her grandson taking his rightful place in the House of Lords. In a shocking moment, she shoots him directly in the chest, but he survives thanks to a hidden piece of armor.
As events unfold, Sherlock arrives at Scotland Yard, where Lestrade poses questions regarding how he was able to solve the case, along with a particular inquiry about Enola's contributions to the investigation. A heart-wrenching farewell ensues between Enola and Tewkesbury as she deciphers a newspaper message, only to realize it wasn't from her mother, but rather a summons by Sherlock to bring her out of hiding. Eventually, while lurking as a newsboy, she overhears Sherlock and Mycroft discussing her future, with Sherlock expressing a desire to become her guardian.
Upon her return to her lodgings, Enola discovers her mother has returned, and they embrace warmly. Eudoria reveals her reasons for leaving, explaining her mission to advance the reform bill, which Enola has championed on her behalf. Yet, she informs Enola that her work isn't over and that she must leave again—though she proudly acknowledges the remarkable individual Enola has become. In the end, Enola realizes she has fully embraced her calling as a detective and a seeker of lost souls, stepping into her own story of freedom and purpose.
