Rio Conchos unfolds in Texas, shortly after the end of the Civil War. A group of four men led by ex-Confederate soldier Major Jim Lassiter (Richard Boone) sets out across the desert on a secret mission to prevent an unbalanced ex-Confederate colonel from selling a cache of stolen rifles to a band of warrior Apaches. The ex-Confederate colonel hopes to supply the renegade Indians with rifles in an attempt to recruit their help in carving out a chunk of Confederate territory in the West. The conflicts among the four men make this a provocative and engaging film.