The Devil Rides Out: In 1930s London, Duc de Richleau and Rex van Ryn rescue their friend Simon Aron from a devil-worshipping cult. Rex falls for a woman named Tanith and takes her away from the cult. The group's leader comes after them, and there is a desperate struggle to defeat the Angel of Death and escape the cult leader, Mocata.
To the Devil a Daughter tells the story of a group of practicing Satanists who disguise themselves as "The Children of the Lord." Catherine—a nun—is one of this group. She is allowed to come home once a year on her birthday. On one of these trips home, an occult writer named John Verney realizes that the group are Satanists and are preparing Catherine to become an avatar of Astaroth on her 18th birthday.
Gateway to Hell sees the return of characters from The Devil Rides Out. Rex van Ryn steals more than a million dollars from his family bank and vanishes in Buenos Aires. Rex's friends have suspicions about the ex-SS Gruppenführer with whom he is said to have been consorting; they find themselves pursuing Rex to the Bolivian Andes and confronting Satanist forces once again.