When word reaches a U.S. Cavalry command that an Apache chief's son is planning an attack on Fort Yuma, a column of soldiers led by Lt. Ben Keegan is sent to deliver ammunition and supplies.
Accompanying them is missionary Melanie Crown, an educated and enlightened woman from the East who despises prejudice and strongly believes everyone can live together in harmony, and the sergeant's sister, Francesca, whose mutual attraction with Keegan is complicated, considering his views.