In solving the mystery of two medallions missing from an inherited curio collection, the Hardys wind up in a desolate area of Guatemala at the mercy of dangerous thugs.

With only the slender clue of an arrow-shaped tie clasp, Frank and Joe Hardy pick up the trail of the cunning gang of thieves responsible for a wave of jewelry-store holdups. But their investigations are interrupted when a desperate plea for help comes from their widowed cousin who lives on a cattle ranch in New Mexico. Frank, Joe, and their pal Chet Morton fly there immediately. The mysterious disappearance of one cowboy after another has given Crowhead...

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...

Frank and Joe, the Hardy boys, solve a mystery involving a magician, American secret agents, and international spy ring, and a Scottish castle.