Fenton Hardy the famous private detective and father of the Hardy Boys asks his sons to help him with his latest case involving the illegal drug trade. Hardy sends Frank and Joe to a house on the cliff whose location offers an excellent vantage point to watch for smugglers.

The Hardy Boys are tricked into going inside the house by cries for help and find themselves trapped for a short time in the attic; meanwhile their telescope and motorcycles are damaged. From the attic they see a man in a motorboat being chased by another motorboat. After his boat explodes in flames Biff and Joe swim out while Frank and Chet get a rowboat to rescue the man. Once brought to shore the man regains consciousness and says his name is Mr. Jones which the Hardy Boys believe to be a thinly-disguised alias.

The next day both Mr. Hardy and Mr. Jones disappear. Frank and Joe seek out one of Mr. Hardy's informants at the docks to see if he knows anything about the smugglers and what might have happened to their father and Mr. Jones. Another top notch mystery for the Hardy Boys to solve.