Rocky Linfield and Jerry Morgan have both lost their fathers in war. In 1952, they meet in the small coastal town of Crafton, Maine, and become best friends pitted against spies seeking information about the first US nuclear submarine. The story begins with Rocky and Susan, Rocky's younger sister, selling books to Mr. Waicukauski, who runs the lighthouse and the library. The youngsters are visiting their grandmother, Martha Makler, in Crafton a few weeks before school starts. The adventure takes the boys and their families into the backwoods of Maine and armed confrontation with the spies.