THE GREAT AIRPORT MYSTERY
While driving home the Hardy boys take a shortcut which results in a strange car crash and an encounter with an unfriendly stranger. The next day they are hired by Mr. Allen, the president of Stanwide Mining Equipment Company, under the guise of being factory messengers when in fact they are working undercover to investigate missing shipments of expensive mining equipment containing platinum.
The Hardy boys decide to quit their messenger jobs when it becomes clear that the gang is onto them. Instead they rent a plane and take aerial photographs of the area where their car crash occurred, however, their camera and exposed film are stolen before they have a chance to develop the pictures. Continuing to investigate the theft of their camera, as well as the theft of the mining equipment, they repeatedly see footprints and hear voices belonging to Clint Hill, an aircraft pilot who is presumed dead after his plane crashed into the ocean, causing them to wonder if his ghost is somehow involved in the thefts.
After recovering their pictures the Hardy boys rent a helicopter and return to the area of the car crash, finding a large hidden cave and recovering the stolen shipments of equipment. Next the Hardy boys fly to a small Caribbean island, and then to Montana in pursuit of the criminals.
Eventually they manage to apprehend all of the criminals involved and return to Bayport gratified at solving yet another mystery.