Stephen Mangan Sir Arthur Conan Doyle Actor Michael Weston Harry Houdini Actor Rebecca Liddiard Constable Adelaide Stratton Actor Andrew Bicknell Exorcist Guest Star Ewen Bremner Sherlock Holmes Guest Star Emily Carey Mary Conan Doyle Guest Star Risteard Cooper Charles Doyle Guest Star James Fleet Dr. Pilsen Guest Star Tiago Alexandre Fonseca Cave Dweller Guest Star Martin Gledhill Lunatic Guest Star Stacey Gough Head Guard Guest Star Charlotte Hope Molly Morgan Guest Star Noah Jupe Kingsley Conan Doyle Guest Star Lewis McGowan Young Doyle Guest Star Chu Omambala Dr. Randall Guest Star Chook Sibtain Dr. Chandra Guest Star Joe Sims Nathaniel Guest Star David Shore Executive Producer Kenton Allen Executive Producer Matthew Justice Executive Producer Luke Alkin Executive Producer Christina Jennings Executive Producer Maggie Murphy Executive Producer Scott Garvie Executive Producer