Under the secret leadership of "The Master Key," Nazi agents kidnap Professor Ellwood Henderson (Bryron Foulger) to get their hands on his latest invention, which extracts gold from seawater. It's up to government operative Tom Brant (Milburn Stone), a police detective (Dennis Moore) and a journalist (Jan Wiley) to recover the scientist and the stolen merchandise. Russell Hicks and Addison Richards co-star in this thrilling 13-episode serial.