Skip's and Harvey's exploits on Tree House Island have become famous enough for Mr. Kemberley, the owner of Cutlass Island to offer the boys a job investigating the island and its caretaker, John Hurd. On a recent visit to the island, Mr. Kemberley had become concerned with John's withdrawn manner. The boys disguised as handymen arrive at Cutlass, a veritable museum of Civil War relics, property of the Kimberley family for years. They are ill prepared for the rigorous program of physical labor cut out for them. Harvey's keen intellect is responsible for uncovering the first bit of evidence indicating John Hurd's involvement in illegal doings. He is also responsible for a seemingly outlandish plan to outwit their captors once the boys are taken prisoners by a group of embezzlers. The Civil War equipment, shelved for posterity, is used in a final round of active duty as the boys protected by antiquated weapons turn the tables and make their way to safety. A typical Scott Corbett adventure -- not to be tested against reality every moment -- but filled with natural boy appeal.