Hidden Highway — Tom Lichtenberg

Sharad LeMaster ran away from his own cult, and tried to hide from his followers by taking a desk job in a motel in the middle of nowhere, but when a certain lazy ghost from his past reappears, Sharad is lured into a haunted house and becomes the proud possession of the witch Eugenia, and gets caught between rival black-market magic-potion dealers in their fight over a girl who just happens to possess the most perfect skull ever for turning into a shrunken head.