Danger is the name of the game when the Hardys agree to help their pen pal from Greece, Evan Pandropolos, search for a priceless, ancient Greek helmet. Years ago, Evan’s uncle had loaned it to Hollywood movie company for use in a silent motion picture, but the treasured helmet had been lost. Picking up foes along the way, the young detectives unearth clues that keep them constantly on the move—from their Greek college campus to California and finally to Greece.

The Hardy brothers' visiting Greek pen pal enlists their help in searching for a priceless ancient Greek helmet loaned to and lost by a Hollywood movie company years before.

ANOTHER ADVENTURE STORY STARRING THE HARDY BOYS, PACKED WITH MYSTERY AND ACTION.

A mission for ATAC has Frank and Joe Hardy traveling the world. The teenage son of a prominent mid-eastern diplomat has gone missing on the Caribbean island of St. John, and the boys take off to find him. Turns out he's been kidnapped by a group involved in a scheme to rob a sunken Spanish galleon of its treasures and sell them on the black market. Frank and Joe search high and low--fighting thugs and sharks--for clues. When the Hardys finally find their quarry, there's another problem --he turns out to be the mastermind of the ring, not its victim!

Frank and Joe are working on a new case...and it just might blow them away! The exclusive Billington Resort in Phoenix, Arizona has two high-profile events on Saturday: a vintage car auction and a celebrity wedding. They also have something they didn't sign up for: a bomb threat. Frank and Joe have just eight hours to find the bad guys and the bomb. If they fail to do so by 3:00 PM, the entire resort will be blown to bits.

Frank and Joe try to prevent the theft of a valuable collection of diamonds from a show.

During Mr. Hardy’s investigation of a ruthless gang of terrorists, Frank and Joe witness an explosion in the sky near an airborne dirigible owned by Quinn Air Fleet. The young detectives look into a clue that takes them into a new animal park outside Bayport, where they are lured into a trap by an unknown enemy. Problems arise for the park owner as he receives pressure from a competitor and a real-estate firm to sell out. Strange occurrences at the park also frighten the visitors and animals. Frank and Joe take up the case despite fore warnings.