John Wayne stars as ex-Union Colonel John Henry Thomas, a free agent now that the Civil War is over. With others who had been in his unit, he sets out to round up thousands of wild horses to sell to the government of the Mexican Emperor in order to make some money before going home. Along the way, he encounters ex-Confederate Colonel James Langdon (Rock Hudson). Langdon is leading a group of Confederates who have no desire to live under the Stars and Stripes and, having lost their property to carpetbaggers, have chosen instead to set out with their families for Mexico.
The two men and their respective groups cross paths on a number of occasions, developing first a grudging truce and later a good-humoured respect, aided by their successful combined defence against a group of bandits. Eventually reaching Mexico they part company, Thomas to sell his horses to the Emperor and Langdon to the town where his group are expected. However, the welcome Langdon's people get is not what they expect. The town has been taken over by Mexican rebels fighting the Emperor, who take the Confederates hostage. They send Langdon to see Thomas with a message that they will start executing Langdon's people unless Thomas brings them the horses instead. These two who were once enemies must now work together if they are to save the Confederates.
It's not really much of a plot, but in this case it matters little this film isn't meant to be great drama but great entertainment. Humour is the mainstay of the film, with action and thrills enough to keep it interesting. Legends John Wayne and Rock Hudson are suitably heroic, but also clearly enjoy working together much of the humour is helped along by the chemistry between the two. At times, the film descends almost to slapstick, most notably during the fistfight at the Fourth of July party, but it's genuinely funny rather than silly. What comes across most clearly is that the cast are having fun making this movie, and that cheerful enthusiasm infects the audience.