Frank, Joe, and Chet are off to Gull Island where Chet's sister has been kidnapped! They follow her trail through alligators and shark-infested waters, into a deadly conspiracy.
Frank and Joe fight for their lives when they find the plane carrying a man who has connections to vital national security information has been sabotaged.
Someone is rigging the boats slated to race in the Northeast National Offshore competition, and with so many lives at stake, Joe and Frank Hardy rev up their own engines to find the saboteur.
Frank and Joe uncover a coded message that points to big trouble in the local circus. Someone in the circus wants to make the boys disappear permanently.
The owner of the Sky Blue Inn asks Frank and Joe to commit a fake crime for the benefit of his guests. Unfortunately, a real robbery occurs, and the Hardy boys get the blame.
Frank and Joe investigate when a string of suspicious accidents and equipment failures threaten to put a company which manufactures computer-operated automobiles out of business.
