Frank and Joe unravel two mysteries, one involving a counterfeiting case and the other concerned with a national security case their father is working on.

The Hardy brothers try to find out who is behind a rash of automobile thefts that are occurring on Shore Road just outside of Bayport.

On an ice-bound, snow-covered island, Frank and Joe attempt to solve the mystery of a boy's disappearance and the theft of a priceless collection of antique medals.

When new team members are being kidnapped and threatened, Frank and Joe join the basketball team at the request of their principal to uncover the culprits.