Bøker utgitt av GROSSET DUNLAP

Once again Frank and Joe Hardy take on a puzzling case when their famous detective father asks the boys to assist him in tracking down a notorious jewel thief and his accomplices. The trail leads to the outskirts of the Hardys' home town and to a weirdly guarded mansion on the old Perth estate. With their pal Chet Morton, the brothers must tackle the mystery of the mansion heir's sudden death. A disappearing floor, a huge, savage-looking, hound, a galloping ghost, and a college professor's startling invention are just a few of the strange elements that complicate the boys' efforts to solve both mysteries.

Frank and Joe race against time to retrieve a scientist's top-secret invention before thieves get their hands on it. But the young detectives soon discover that they are involved in a mystery far greater in scope than just safeguarding the invention. When Joe is kidnapped, this incident starts Frank of on a chase that could end disastrously for him and his pals.

Triggered by the disappearance of a brilliant young professor, this mystery takes the Hardy boys first to Kenworthy College, where they find a puzzling message on an examination paper. But then, a new clue is unearthed that sends the young detectives to the Honeycomb Caves. After many dangerous encounters, Frank and Joe discover a powerful searchlight in one of the craggy caverns along the seacoast. In the brilliant white glare of the searchlight, the startling secret of the caves is dramatically revealed.

When the Hardy Boys eagerly agree to assist their friend Jack Dodd and his father in locating a family treasure, the two young detectives are unaware of the baffling complications that will arise. Deadly road traps, aerial ambush, a spider man and a suspect who carries a menacing cane harass the young detectives as they seek the triple solution to this perplexing and exciting mystery.