The Mystery of the Shrinking House (1972) - Front cover of ''The Mystery of the Shrinking House''.The Mystery of the Dead Man's Riddle (1974) - Front cover of ''The Mystery of the Dead Man's Riddle''The Mystery of the Silver Spider (1967) - Front cover of ''The Mystery of the Silver Spider''.The Mystery of the Talking Skull (1969) - Front cover of ''The Mystery of the Talking Skull''.The Mystery of the Screaming Clock (1968) - Front cover of ''The Mystery of the Screaming Clock''.The Mystery of the Coughing Dragon (1970) - Illustration for the Danish release of ''The Mystery of the Coughing Dragon'' by artist Peter Madsen.The Secret of Skeleton Island (1966) - Front cover of ''The Secret of Skeleton Island''.The Secret of Terror Castle (1964) - Front cover of ''The Secret of Terror Castle''.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 Singing Serpent (1972) - Front cover of ''The Mystery of the Singing Serpent''.The Mystery of the Dancing Devil (1976) - Front cover of ''The Mystery of the Dancing Devil''.The Mystery of the Invisible Dog (1975) - Front cover of ''The Mystery of the Invisible Dog''.The Mystery of the Vanishing Treasure (1966) - Front cover of ''The Mystery of the Vanishing Treasure''.The Mystery of the Talking Skull (1969) - Front cover of ''The Mystery of the Talking Skull''.