Capt. Harper's cavalry patrol returns to the fort to find it besieged by Ute Indians. The apparent cause is the recapture of Army traitor Brett Halliday, who deserted to the Utes in a previous war; but Brett has a different story. With capture imminent, the only chance for the surviving men (and one woman) is to boat down a wild, uncharted river, where Harper and Halliday must pull together, like it or not.