Terence Fisher's thrilling screen adaptation of Dennis Wheatley's classic novel centres on the age-old battle between the forces of good and evil. Employing ancient rituals, a group of Satanists invoke the powers of darkness for personal gain, risking very souls to do so. All those involved become increasingly ensnared by the malevolent presence they have summoned. Learning of a friend's involvement, the Duke de Richeleau (Christopher Lee) enters the fray as champion for the Powers of Light. Accompanied by his three friends, Rex Van Ryn (Leon Greene), Simon Aron (Patrick Mower) and Richard Eaton (Paul Eddington), the Duke takes the battle to the enemy... the very Devil himself!