The story begins with the Hardy boys, Frank and Joe, and their friend Chet Morton enjoying winter activities on Barmet Bay. They decide to explore Cabin Island, a desolate place with a history of being uninhabited. Upon arrival, they encounter a surly man named Elroy Jefferson, who orders them off the island, raising their suspicions. The boys later learn that Jefferson is an antique dealer and the owner of the island. After a series of events, including a close call with two troublemakers, Tad Carson and Ike Nash, the boys discover a mysterious notebook belonging to John Sparewell, a former servant of Jefferson who disappeared years ago along with a valuable stamp collection. The notebook contains a cipher that hints at something hidden in the chimney of the cabin. As they investigate, a storm causes the chimney to collapse, revealing the rosewood box containing Jefferson's long-lost stamp collection. Hanleigh, the man who had previously chased them off the island, returns, but the boys confront him and learn about his connection to Sparewell. They decide to return the stamps to Jefferson, who rewards them for their efforts and allows them to use the cabin whenever they wish. The story concludes with the boys reflecting on their adventure, the mysteries they uncovered, and the friendships they strengthened during their time on Cabin Island.
By Franklin W. Dixon · First published 1939 · Genre: Mystery, Adventure, Young Adult · 25 chapters