Great condition for its age. Published 1967. Some wear on cover, especially along the top of the cover edges. The cover looks to be separating slightly on the inside (see photo). Some yellowing and age spots throughout. Clean pages. 'Frank and Joe race against time to retrieve a scientist’s top-secret invention before thieves get their hands on it. But the young detectives soon discover that they are involved in a mystery far greater in scope than just safeguarding the invention. When Joe is kidnapped, this incident starts Frank off on a chase that could end disastrously for him and his pals.'