In the closing days of the American Civil War, Union Army Colonel John Henry Thomas (John Wayne) and company organize one final attack on a small unit of Confederate soldiers, only to be informed after bloodily defeating them that the war had ended three days ago at Appomattox Court House National Historical Park in Virginia. Saddened and weary, Thomas leads his men out west towards home with the intention of rounding up and selling wild horses in the Arizona Territory and New Mexico Territory to compensate them for their loyalty, friendship, and war service. Meanwhile, a band of Confederate Army soldiers led by Colonel James Langdon (Rock Hudson) feel the war has left them with no home, and they prepare to emigrate south to Mexico and serve as reinforcements to Emperor Maximilian I of Mexico, leader of the French intervention in Mexico against the republican government of President Benito Juarez. Langdon torches his plantation home before he departs rather than seeing it fall into the hands of Northern carpetbaggers. At the same time, Thomas and the surviving members of his command meet up with Thomas' adopted Indian son, Blue Boy (Roman Gabriel), and other members of his tribe from Oklahoma Territory. Together they round up a herd of 3,000 horses and take them across the Rio Grande for sale to Maximilian's representatives in Durango, Mexico.