Joe Bass, an American fur trapper, is making his way back home with a full cargo of hides when he encounters a group of Kiowa Indians led by Two Crows (Armando Silvestre), who insist on taking his furs. As "payment" they offer him a slave, Joseph Lee (Ossie Davis), who they had previously taken from a group of Comanches. Reluctantly, realising he cannot fight them, Bass agrees to the trade. Bass is slightly bemused by his new companion, who is a well-educated and refined house slave, unused to the ways of the West. Bass orders him to help him recover the furs from the Kiowa. Lee only agrees to help if Bass agrees to take him to Mexico where slavery is outlawed. Bass is not amused, but the two strike up a friendly relationship, with Bass teaching Lee how to catch food in the West. As Lee and Bass come upon the Kiowa, they watch them being ambushed by a group of scalphunters, white Americans and Mexicans who were offered a bounty by the government for each Native scalp they brought in. These scalphunters, led by Jim Howie (Telly Savalas), kill the Kiowa and also steal the furs which Bass had hoped to recover. He and Lee are forced to track the party, hoping to take back the furs. Unfortunately, while spying on them, Lee tips over a cliff and is captured by the scalphunters. As they travel southwards, Jim Howie's girlfriend, Kate (Shelley Winters), reveals to Lee that they are heading for Mexico. He begins to win her favor, by doing her hair and telling her fortune, hoping she will persuade Howie to take him with them across the border, rather than sell him. Bass meanwhile has been following closely on their trail, and at one point he pins them down with sniper fire, forcing them to let loose the packhorse carrying the furs. He is ambushed, however, and the scalphunters recover the furs and proceed on their way. Approaching their camp at night, Bass tries to persuade Lee to help him, but the slave is now set on going to Mexico and refuses him assistance. Bass kills several of the scalphunters, by intentionally starting a rock avalanche in the mountains near where they are situated. After again failing to secure the furs, Bass contaminates the water of a nearby creek with a toxin that causes the scalphunters' horses to run and buck wildly as they drink the water. Now thoroughly fed up, and wanting to make it to Mexico in safety, they send Lee as a courier to Bass telling him he can keep the furs.