Fort Bravo is a Union (American Civil War) prison camp with a strict disciplinarian named Captain Roper (William Holden). A pretty woman named Carla Forester (Eleanor Parker) shows up to help with a wedding of her friend but is really there to assist in freeing some prisoners including her previous beau Confederate States of America Captain John Marsh (John Forsythe). Roper falls in love with her (and she with him) and the escape happens after the wedding celebrations and Carla goes with the 4 confederate escapees. This gives Roper an additional motive to recapture the escapees. He does just that, but on the way back to the fort, they are attacked by fierce Mescalero Apaches who are hostile to both sides and the group ends up trapped in a shallow exposed depression. Roper frees and arms his prisoners, but even then, it looks like the Apaches will wipe them out. Bailey (John Lupton), a proven coward, escapes when one of their loose horses returns in the night. One by one, the rest of the group are killed, including Campbell (William Demarest), Young (William Campbell (film actor)), and the Kiowa guide. Marsh and Lieutenant Beecher (Richard Anderson) are wounded. The next morning, to try to save Carla, Roper makes it look like he is the only one left alive and walks out in plain view. He is wounded, but the cavalry comes to the rescue just in time. Roper thanks Bailey for coming with help, while Marsh dies after smiling at Bailey who has come through and shown he is not a coward.