The story begins with the Hardy boys and their pal
Chet Morton returning to
Bayport on a small coast liner from Larchmont where they had procured handwriting samples from Miss Pennyweather for a case on which their father,
Fenton Hardy, was working. During a storm, they meet Mr. Samuel Blackstone who tells the boys that he is carrying a large sum of money. Shortly thereafter, the ship runs aground and Mr. Blackstone is knocked down and badly hurt.
Joe and Chet manage to swim to shore but Frank Hardy goes missing as he stayed behind to assist the injured Mr. Blackstone. Shortly after Frank is located, the three boys are arrested on charges of robbing Mr. Blackstone. The Hardy boys immediately suspect Mr. Ruel Rand of robbing Mr. Blackstone and set out to track him down. Recording the license plate of a car that they see him get into, they learn he lives in Hidden Harbor. The Hardy boys visit the wreck of the
Resolute where they attempt to retrieve the handwriting samples. However, their boat drifts off and they are detained by the Coast Guard before they are able to reach their
stateroom. After returning to land, they are questioned by the
district attorney at Mr. Blackstone’s bedside. There they learn about the long-standing feud between the Blackstones and the Rands. Chet and the Hardy boys travel south to Hidden Harbor to retrieve new handwriting samples from Miss Pennyworth as well as to investigate who stole Mr. Blackstone’s money. While there, they are followed by a detective and their campsite is vandalized. They also stumble across a ‘secret society’ of young black men being led by Luke Jones, a servant to Mr. Blackstone. This group of Negroes kidnaps Mr. Rand’s mentally insane brother who manages to turn the tables on them by stealing their revolvers. Eventually, the Hardy boys manage to find and disarm the brother. They also capture Luke Jones and make him confess to stealing Mr. Blackstone’s money and his diamond ring. He further admits to being responsible for inciting more hatred between the two families. The Hardy boys also manage to gather indisputable evidence which solves their father’s case without the need for replacement handwriting samples. ==References==