Fritz has just arrived in a place so secret it isn't shown on any map. Even mentioning its name is forbidden. Mail is censored. Visitors are not allowed.
When Fritz—known as Franklin until he came here—learns that this remote spot in the New Mexico mountains is the site of a heavily guarded government laboratory, his curiosity takes over. Exactly what are his father and other scientists working on at the lab? It's common knowledge that their top-secret project has something to do with the war in Europe and the Pacific, but what? Fritz is determined to find out. With the help of Kathy, his seventh-grade classmate, Fritz searches for clues. He records each observation and every rumor in a notebook he doesn't dare let out of his sight.
His sleuthing—and trying to avoid, evade, or outwit the two bullies who have it in for him—keeps Fritz busy. But he finds time to explore the area with his Spanish-American friend Manny, to become involved in a prank with unintended consequences, and to get into serious trouble when he and Manny show too much interest in a restricted area.