A disgruntled settler kills an Apache chief at Fort Yuma, and the fort's commander knows that the chief's son, Manga Colorado, will seek revenge and go on the warpath. He sends word by a courier to Fort Apache where a supply column is due to head across the desert to Fort Yuman, but the courier is killed by Mangas. The column, under the command of Lieutenant Ben Keegan who hates Apaches because he doesn't trust them, and because his assigned scout is Jonas, the brother of an Apache girl, Francesca, whom Keegan has been having an affair with. Also accompanying them is Melanie Crowne, who is going to do missionary work among the Apaches. Mangas attacks the column wiping out everybody but Keegan, Jonas and Melanie. Francesca is killed while trying to warn Keegan, and he realizes how foolish he had been in his prejudice and in keeping his love secret. The Apaches, dressed in the uniforms of the dead soldier, plan to gain entrance to Fort Yuma and massacre the men there.