On Christmas Day 1884, a desperate plea from a mysterious woman leads Arthur Conan Doyle—struggling physician, aspiring writer, and part-time demystifier of the occult—to a seance in London’s East End and into a fiendish and deadly trap. Stunned by a shocking display of black magic, Doyle witnesses a murder, nearly falling victim himself before being rescued by a secretive stranger: Jack Sparks, a man who claims to be special agent to Queen Victoria. He tells Doyle that he has been targeted by a diabolical coven of Satanists—the Dark Brotherhood.

As they track their attackers across the length and breadth of Britain, assailed by forces of darkness both human and supernatural, Conan Doyle and Sparks unmask a terrifying conspiracy that threatens not only the Crown but the very fabric of modern civilization. Their only clue: a list of seven names, the leaders of the Brotherhood.

Skeptical by nature and profession, Doyle labors to prove that the events he has witnessed—horrifying visions, zombies, ghouls, molecular alteration—are elaborate ruses with logical explanations. But if so, why? Simply because Doyle’s anti-occultist writings, never even published, have inadvertently exposed the Brotherhood’s intentions? Who is the elusive, seemingly superhuman mastermind behind the Seven? Most important, as Doyle continues to put his life in the hands of Jack Sparks, the question persists: Can Sparks be trusted?