Frank and Joe Hardy are the sons of Fenton Hardy, a famous private detective. Finding everyday life at home in Bayport dull, the boys hope their father will let them work on one of his cases. Disappointed when he tells them his work is too dangerous for children, they are more determined than ever to follow in their dad's footsteps, and solve mysteries.
| Actor | Role |
|---|---|
 Tim ConsidineFrank Hardy | Frank Hardy |
 Tommy KirkJoe Hardy | Joe Hardy |
| FFlorenz AmesSilas Applegate | Silas Applegate |
 Russ ConwayFenton Hardy | Fenton Hardy |
 Sarah SelbyAunt Gertrude | Aunt Gertrude |
 Robert FoulkJackley the Plumber | Jackley the Plumber |
| CCarole Ann CampbellIola Morton | Iola Morton |
| DDonald MacDonaldPerry Robinson | Perry Robinson |
 Arthur ShieldsBoles - Ex-Gardener | Boles - Ex-Gardener |
 Charles CanePolice Sergeant | Police Sergeant |
 Frances MorrisLandlady | Landlady |
| BBrick SullivanPoliceman | Policeman |
 Mort Millspoliceman | policeman |
 Don C. HarveyPoliceman | Policeman |
 Dan SturkiePolice Detective | Police Detective |
 William HenryPoliceman | Policeman |
| JJess KirkpatrickPoliceman | Policeman |