Enola starts her detective agency but struggles to get clients, unlike her famous detective brother Sherlock Holmes. A factory girl named Bessie asks Enola to help find her missing sister Sarah Chapman. Bessie takes Enola to the match factory, which is experiencing a deadly typhus epidemic and encounters Mae, who worked alongside the sisters.

Enola follows Mae to the Paragon Theatre, where Mae and Sarah work as dancers. She finds a letter written to Sarah by a secret lover. On her way home, Enola comes across a drunken Sherlock and brings him home to 221B Baker Street. He is struggling to solve his latest case involving the blackmail of government officials, but he cannot trace the owner of the accounts where the money is sent.

Enola deduces that the poem is a code leading to a home in Whitechapel; there, she finds Mae dying of a stab wound. Enola discovers a piece of sheet music in Mae's dress but is interrupted by Superintendent Grail who accuses her of murder.

Enola escapes to Sherlock's flat and deduces that Sarah's lover will be at a ball hosted by the Lyon family. There, she meets Cicely, a friendly noblewoman, and Mira Troy, secretary to Treasury Minister Lord Charles McIntyre. Enola meets Tewkesbury, who teaches her how to dance so she can find an opportunity to get closer to William Lyon, the son of the match factory's owner and Sarah's lover.

Meanwhile, Sherlock pieces together a message in the blackmail scheme from its mastermind, Moriarty. Enola is arrested by Grail before she can speak with William, but Sherlock enlists their mother Eudoria and her fellow radical suffragette Edith to break Enola out of prison.

While visiting Tewkesbury, Enola realizes that Sarah is Cicely and that she, Mae, and William had discovered that white phosphorus, not typhus, was killing the workers and were planning to expose it. Tewkesbury and Enola confess their love for each other and head to the factory, where they meet Sherlock and find William dead with a corner of the sheet music. The three deduce Lord McIntyre had struck a deal with William's father to use cheap phosphorus to increase profit.

The group heads to the Paragon after realizing the full sheet music was a map of the theatre. There, Sarah confirms Enola's findings and admits she and William needed Tewkesbury's help to expose McIntyre. Grail and several policemen arrive and a fight ensues, resulting in Grail's death.

Lord McIntyre arrives with Lestrade. He burns the evidence of the dealings and attempts to have Sarah arrested, but Sherlock and Enola deduce that Mira Troy is Moriarty and is responsible for the blackmail and murder. Mira is taken into custody.

Sarah, Bessie, and Enola inform the factory's match girls of the events and convince them to strike. McIntyre is arrested with Tewkesbury's help, while Moriarty escapes police custody. Enola sets up a new office at Edith's shop; Tewkesbury has begun courting her in earnest, and he invites Enola to a ball.^[3]