As related in the first volume of this series, "The Hardy Boys: The Tower Treasure," Frank and Joe Hardy were the sons of Fenton Hardy, a private detective of international fame. Mr. Hardy, who had been for many years on the New York police force and who had later resigned to carry on a private detective practice, was a criminologist of note. He knew by sight and by reputation most of the notorious criminals of his day, and his mastery over all the branches of his profession was such as to place him at the very forefront of American detectives. So great had been the demand for his services in solving the mysteries of crimes that had baffled the detective forces of other cities that he had found it much more lucrative to carry on a practice of his own than to remain attached to the service in any one city, even such a city as the great American metropolis. Fenton Hardy, with his wife, Laura Hardy, and their two sons, Frank and Joe, had accordingly moved to Bayport, a city of about fifty thousand inhabitants, situated on Barmet Bay, on the Atlantic Ocean. There Frank and Joe had gone to school until now they were in the Bayport high school. Both boys were fully conscious of the fame of their father and were eager to follow in his footsteps, although their mother had expressed a desire that they fit themselves for some less hazardous and more conventional profession. However, the Hardy boys had inherited much of their father's ability and deductive talent. Already they had aided in solving two mysteries that had kept Bayport by the ears. As related in "The Hardy Boys: The Tower Treasure," they had solved the mystery of the theft of valuable jewels and bonds from Tower Mansion, after even Fenton Hardy himself had been unable to discover where the thief had hidden the loot. In the second volume of the series, "The Hardy Boys: The House on the Cliff," has been told how the Hardy boys discovered the haunt of a gang of smugglers who were operating in Barmet Bay. In this case they had received a substantial reward, as Federal agents had tried in vain to locate the smugglers' base of activities for many months. Following the adventures at the house on the cliff an uneventful winter and spring had passed, the brothers devoting themselves to their studies and to an occasional winter holiday. Christmas had come with many presents, and now warm weather was once more at hand. Because of the pride they took in their achievements as amateur detectives, the Hardy boys felt very keenly the ignominy of being so easily fooled by the stranger who had passed the counterfeit money upon them. "Dad will have the laugh on us now," muttered Joe, as they heard the distant whistle of the approaching train. "Well, we'll tell him about it, anyway. Who knows but what a big case might arise out of this?"