The Second World War has changed life at Union Lake, Michigan. At age ten, Jimmy has a paper route. One of his subscribers wants Jimmy and his friend Ralph to clean her garage. While cleaning out an old trunk, Jimmy finds a newspaper article from 1932 that tells of two robberies. He also discovers a letter written by one of the robbers to his partner. The stolen money is buried on an island next to a Y-shaped willow tree. Jimmy lives in a county with many lakes and his search for the island leads him from lake to lake and many breathtaking adventures.
Jimmy's friend Ralph wants to win a bet with his older brother on the number of fish they can catch. He also wants to bend the rules to win his bet. Will a sudden storm and a new device help or hinder their efforts to catch fish?
Readers that like a good mystery, a carefully crafted school prank and the summer escapades of Jimmy and Ralph will enjoy 'Jimmy and the Secret letter.'