The Hardy boys dial a wrong number, get the Pentagon, and suddenly find themselves in a dangerous adventure involving national security.

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, their father is investigating the baffling thefts of mercury shipments occurring along the Atlantic seaboard. The celebrated detective finds himself up against a murderous gang who nearly dispose of him in a cask at the bottom of Baltimore harbor. Frank and Joe's astute sleuthing ability not only saves Mr. Hardy's life, but also links the mercury thefts to the top-secret Super S missile mysteriously stolen from a government arsenal. In a race against time the three Hardys foil a diabolical scheme to create widespread havoc in the United States. Pulse-pounding excitement fills every page of this suspense thriller. - Flyleaf.