While searching for the guard end of a broken saber that will solve one mystery, the Hardy brothers become involved with a gang of bank robbers.

An assignment form their famous detective father to track down a ring of credit-card counterfeiters takes Frank and Joe Hardy on an exciting camping trip to the Rocky Mountains. But the cross-country trek with their pals Chet Morton and Biff Hooper is jinxed from the very first day. Strange happenings on a nearly impassable mountain lure Frank, Joe, Chet, and Biff to almost certain death before they discover the sinister reason for the danger on Vampire...

Frank and Joe Hardy become involved in a case affecting national security when Joe dials a wrong telephone number and gets the Pentagon. Two words— “Bombay Boomerang”— that the boys hear before the line goes dead plunge them into a whirlpool of danger and intrigue. At the same time, Frank and Joe must save their father from a murderous gang stealing mercury shipments in the Baltimore harbor. With clues linking the mercury thefts...

The launching of the Firebird Rocket is endangered when a famous rocket scientist disappears without a trace on his way to the Woomera Monitoring Station in Australia. Assigned to the case, Fenton Hardy tells his sons he needs their help. And Frank and Joe must turn down a request that they find the missing son of a prominent senator. With courage, wit, and clever detective work, the young detectives begin to close in on the enemy, only to discover...