Fenton HardyFrank and Joe could never keep a secret from their astute father, and they suspected that this was one of the abilities that made him such a successful investigator. Indeed, Fenton Hardy had made an enviable name for himself. For many years he had been a detective with the New York Police Department, but resigned to accept cases of his own. He is now known as one of the best private detectives in the country and has solved many mysteries that had baffled city detective forces.
Frank, a tall, dark-haired eighteen-year-old, is the more serious of the brothers. He likes to think things out, taking into account all aspects of a problem. He's good at analysing clues and figuring out which are the logical steps to take in order to solve a case. According to Mystery of the Flying Express, Frank is a Scorpio.
A year younger than his brother, Joe is almost Frank's complete opposite. He dashes into all kinds of situations without worrying too much about consequences, and refuses to admit that anything is impossible. Joe is full of enthusiasm and good humour, and can always be counted on to lighten up a tense situation with a witty remark. According to Mystery of the Flying Express, Joe is an Aries.
Laura Hardy, a pretty, petite woman, always worries about the dangers her husband and sons face, but has become accustomed to their hectic lifestyle.
Gertrude Hardy, a spinster of "uncertain years," is Fenton Hardy's sister. She never refrains from making her opinions known in the form of long tirades, but her prim visage is deceptive, for beneath her forbidding appearance, she is really one of the kindest people one could ever hope to meet.