Unbroken traces the life of Louis (Louie) Zamperini, an Italian American from California, through his return to the United States and recovery from incarceration as a prisoner of war during World War II. Prior to beginning military service, Zamperini had been an award-winning long-distance runner who participated on the US Olympic team.

The first two chapters follow Louie from birth to the point when he won his first major state-wide track title and set a state record.

As a child, Louis (born 1917) experienced anti-Italian discrimination in Torrance, California, and came down with pneumonia. As a teenager, he grew much stronger but indulged in reckless behavior such as theft. His future looked bleak.

Chapter 2 shows how, with guidance from his big brother, Pete, he turned around when he started sports. Pete became his coach when he joined the high school track team.

As soon as he acquired the discipline to practice regularly, he began to show tremendous promise, making incredibly fast times and winning races. Before long he was breaking high school records and setting new records. He then beat college racers. Chapter 2 ends with Louie, at age sixteen, setting a new course record at the UCLA Southern California Cross Country meet.