Peter O'Toole played Arthur Conan Doyle in the film. He previously played his most famous creation, Sherlock Holmes, in Sherlock Holmes and the Sign of Four (1983), Sherlock Holmes and the Valley of Fear (1983) and Sherlock Holmes and a Study in Scarlet (1983).
Both Florence Hoath and Elizabeth Earl got to meet the daughter of the real Frances Griffiths, Christine Lynch, who was involved with the film's production. Like her mother, she believed the fairies were real too.
Harvey Keitel had previously been attached to play Harry Houdini in the film Ragtime, but he was recast. However, as he had already done lots of research in preparation for that film, he was able to incorporate it into playing Houdini in this one.
Florence Hoath has brown hair, so she wore a red wig to portray Elsie.