The Mystery of the Shrinking House (1972) - Front cover of ''The Mystery of the Shrinking House''.The Mystery of the Coughing Dragon (1970) - Front cover of ''The Mystery of the Coughing Dragon''.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 Monster Mountain (1973) - Front cover of ''The Mystery of the Monster Mountain''.The Mystery of the Headless Horse (1977) - Front cover of ''The Mystery of the Headless Horse''.The Mystery of the Talking Skull (1969) - Front cover of ''The Mystery of the Talking Skull''.The Mystery of the Dead Man's Riddle (1974) - Front cover of ''The Mystery of the Dead Man's Riddle''The Secret of the Crooked Cat (1970) - Front cover of ''The Secret of the Crooked Cat''.The Mystery of the Singing Serpent (1972) - Front cover of ''The Mystery of the Singing Serpent''.The Mystery of the Death Trap Mine - Front cover of ''The Mystery of the Death Trap Mine''.The Mystery of the Flaming Footprints (1971) - Front cover of ''The Mystery of the Flaming Footprints''.The Mystery of the Moaning Cave (1968) - Front cover of ''The Mystery of the Moaning Cave''.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 Coughing Dragon (1970) - Illustration from ''The Mystery of the Coughing Dragon'' by artist Harry Kane.The Mystery of the Deadly Double (1978) - Front cover of ''The Mystery of the Deadly Double''.