The Mystery of the Headless Horse (1977) - Front cover of ''The Mystery of the Headless Horse''.The Secret of the Phantom Lake (1973) - Front cover of ''The Secret of the Phantom Lake''.The Mystery of the Whispering Mummy (1965) - Front cover of ''The Mystery of the Whispering Mummy''.The Mystery of the Flaming Footprints (1971) - Illustration for the Danish release of ''The Mystery of the Flaming Footprints'' by artist Peter Madsen.The Mystery of the Coughing Dragon (1970) - Illustration for the Danish release of ''The Mystery of the Coughing Dragon'' by artist Peter Madsen.The Mystery of the Dancing Devil (1976) - Front cover of ''The Mystery of the Dancing Devil''.The Mystery of the Magic Circle (1978) - Front cover of ''The Mystery of the Magic Circle''.The Mystery of the Green Ghost (1965) - Front cover of ''The Mystery of the Green Ghost''.The Mystery of the Deadly Double (1978) - Front cover of ''The Mystery of the Deadly Double''.The Secret of Terror Castle (1964) - Front cover of ''The Secret of Terror Castle''.The Mystery of the Talking Skull (1969) - Front cover of ''The Mystery of the Talking Skull''.The Mystery of the Magic Circle (1978) - Front cover of ''The Mystery of the Magic Circle''.The Secret of the Crooked Cat (1970) - Front cover of ''The Secret of the Crooked Cat''.The Mystery of the the Fiery Eye (1967) - Illustration for ''The Mystery of the the Fiery Eye'' by artist Harry Kane.The Mystery of the Laughing Shadow (1969) - Front cover of ''The Mystery of the Laughing Shadow''.