Brigadier General Frank D. Merrill leads the 3,000 American volunteers of his 5307th Composite Unit (Provisional), aka "Merrill's Marauders", behind Japanese lines across Burma to Myitkyina, pushing beyond their limits and fighting pitched battles at every strong-point.

Grant MacLaine, a former railroad troubleshooter, lost his job after letting his outlaw brother, the Utica Kid, escape. After spending five years wandering the west and earning his living playing the accordion, he is given a second chance by his former boss.