Donald F. Averill 
The Lighthouse Library [EPUB ebook] 

Ten-year-old Rocky Linfield and eleven- year-old Jerry Morgan met in the small coastal town of Crafton, Maine, in 1952. Both boys have lost their fathers in war and become best friends. Rocky and his younger sister, Susan, meet Mr. Waicukauski, who runs the lighthouse library. They give him a book containing coded information handed to them by a man who is killed on a highway. The Linfield children are visiting their grandmother, Martha Makler, an FBI retiree, while their mother is working in a parachute factory. The adventure takes the children and their families into the backwoods of Maine, where they are confronted by spies seeking data about the first US nuclear submarine.