Sherlock is a 14-year-old student spending the summer of 1868 with relatives in Farnham while his father serves in India. He struggles with isolation from his peers and lacks a close confidant until he arrives at the manor. Armed with a sharp intellect, he eagerly applies himself to learning investigative methods after hearing rumors of a mysterious death.

A 14-year-old orphan who survives by living on his wits in the streets of Farnham. He maintains a scruffy appearance with long straggly hair and dirty clothing. Relying on a horse named Albert and a narrowboat for transportation, he initiates the central investigation by bringing his strange discovery to Sherlock.

An older American man from New Mexico who exhibits a physical vitality that contrasts with his white hair and wrinkled skin. He previously worked as a tracker in the United States and has come to England with the cooperation of the British government. He teaches his pupil the foundational skills of observation and fact-gathering.

A French aristocrat and military veteran who was severely injured during the Crimean War. He harbors a deep resentment toward British colonial ambitions. Currently, he operates a garment factory in Farnham while representing a secretive group called the Paradol Chamber.

Amyus Crowe's 14-year-old daughter. She possesses a bold temperament and resents her relocation to England, blaming the transatlantic journey for her mother's passing. She refuses to stay safely out of the way and insists on actively participating in the ongoing mystery.

Sherlock's older brother, who works for the Foreign Office in London. He acts as the head of the family while their father is stationed in India. He keeps a close eye on his sibling's welfare through correspondence and drops hints about the secret nature of his government work.

The middle-aged housekeeper at Holmes Manor. She maintains a sour disposition and makes no effort to hide her dislike for the visiting nephew. She spends much of her time monitoring the boy's movements and intercepting the household's mail.

The elderly uncle of the Holmes brothers. He operates as a pious scholar who spends his days in the manor's library writing religious tracts and sermons. He remains largely oblivious to the dangerous events unfolding around his property.

An enormous man who serves as the chief enforcer and whip master for his employer. He is ruthlessly pragmatic about executing orders, whether that involves performing mundane servant tasks or enacting violence against intruders.

An elderly relative hosting her nephew for the summer. She appears easily distracted and frequently talks to herself. Unwittingly, she provides a crucial piece of information regarding the employment history of a deceased gardener.

An expert in tropical diseases based in Guildford. He possesses the scientific knowledge necessary to identify a mysterious yellow powder, effectively debunking the local rumors of a bubonic plague outbreak.

A rough worker employed at the local garment warehouse. He actively attempts to sabotage a boat trip by throwing lanterns and attacking the passengers with a knife.

A laborer employed by the local garment factory. He moves mysterious goods for his employer and becomes a severe threat when he spots a familiar face spying on a London warehouse.