Sherlock Holmes is an internationally renowned amateur detective operating out of London. He relies on highly developed deductive reasoning and keen observation skills to solve cases that baffle conventional authorities. He views emotion as a distraction from pure logic, preferring strict analytical thought. To cope with periods lacking stimulating work, he resorts to using cocaine.

Irene Adler is a New Jersey-born opera contralto residing at Briony Lodge in London. She is financially independent and operates outside traditional Victorian social norms for women. Following a past romance with the King of Bohemia, she retains a photograph that threatens his upcoming royal marriage. She possesses sharp intellect and resources that make her a formidable obstacle.

Dr. John Watson is a recently married medical doctor and the narrator of the detective's cases. He serves as a loyal companion who willingly assists with investigations, even if they cross strict legal boundaries. Though highly intelligent, he lacks the specialized deductive reasoning of his friend and often acts as an audience for the detective's deductions.

Wilhelm Gottsreich Sigismond von Ormstein is the hereditary King of Bohemia who travels to London in secret to secure private detective services. He is a tall, physically imposing man seeking to hide a past indiscretion before his public marriage announcement. He views himself as socially superior to others but lacks the cunning to resolve his own extortion problem, resorting to hiring burglars before turning to professional help.

Godfrey Norton is a handsome gentleman lawyer who frequently visits Irene Adler's home in London. His sudden appearances and hasty departures complicate the initial understanding of the social circle surrounding Briony Lodge.

The Princess of Scandinavia is the royal fiancée of the King of Bohemia. Her family maintains strict principles, meaning any hint of scandal or past indiscretions from the King would immediately end the marriage arrangements.