The Devil Rides Out
The Devil Rides Out is a 1934 novel by Dennis Wheatley telling a disturbing story of black magic and the occult. The four main characters, the Duke de Richleau, Rex van Ryn, Simon Aaron and Richard Eaton, appear in a series of novels by Wheatley. The book was made into a film by Hammer Film Productions in 1968. There is also an abridged, young adult version "retold" by Alison Sage for the "Fleshcreepers" series (1987).
Set in 1930s London and the South of England, the Duc de Richleau and Rex van Ryn discover that their friend Simon Aaron has become involved with a cult of devil worshipers headed by the sinister Mr. Mocata. Following a daring rescue from a Grand Sabbat on Salisbury Plain, they take Simon to the country house of Richard Eaton and his wife, the Princess Marie-Lou, where they are besieged by unearthly forces, and discover the true purpose of Mocata's cult.