Peter Perkins (Tommy Lee Jones) is a veteran cowboy who embodies the values of the old West, living in a small Texas town bordering the U.S. and Mexico. He hires Melquiades Estrada as a ranch hand and quickly befriends the man. But when Estrada is gunned down under mysterious circumstances, Perkins takes justice into his own hands and kidnaps a trigger-happy border patrolman (Barry Pepper), forcing Perkins to unearth Estrada's body and accompany Perkins on horseback on the long and treacherous journey through the frontier mountains and back roads of Mexico to bring his friend's body home.