Two boys from different cultures, one a Texan, one a New Mexican, get caught on opposite sides of the U.S. Civil War.
Jemmy Martin wants to stay on the family farm near San Antonio, Texas. When his brother becomes a packer for a regiment of Texas Mounted Volunteers, then deserts, Jemmy takes his brother's identity to protect him from the firing squad. Now all Jemmy wants is to get himself and his family mules back to the farm where they belong.
Raul Atencio isn't interested in the Americanos war. The nephew of a prosperous Socorro, New Mexico merchant, Raul wants to become rich and powerful like his uncle. While at Fort Craig to deliver supplies and help build defenses, the Confederates arrive, and Raul becomes an unwilling participant in the defense of the Fort.
As the Confederate army marches around Fort Craig, the Union forces prepare to stop them. Upon the banks of the Rio Grande the two armies face off in the Battle of Valverde, and both Jemmy and Raul must struggle to keep themselves, and their dreams, alive.