Frank and Joe Hardy receive an unusual assignment from their detective father. They are to "break into" the house of a Bayport neighbor, Malcolm Wright and retrieve a top-secret invention that the scientist had hidden in his study before leaving for California. The invention is in danger of being stolen and the boys race against time to beat the thieves at their own game. The young detectives soon discover that they are involved in a mystery far greater in scope than just retrieving the invention.
"Could be better"
Valuable electronic parts containing platinum are being stolen from shipments made by Stanwide Mining Equipment Company's cargo planes and Frank and Joe Hardy are called upon to assist their world-renowned detective father solve the baffling case. At Stanwide, the boys pose as employees and become suspicious of their boss's hostility towards them. Is he involved in the racket? And what is the truth behind the plane crash at sea in which Clint Hill, chief pilot for Stanwide was killed?
The Hardy Boys are elated over their good luck when wealthy Elroy Jefferson invites them to spend Christmas vacation at his private retreat on Cabin Island. But when Frank and Joe make a reconnaissance trip in their iceboat, The Sea Gull to the island, a belligerent stranger orders them off. Why?