With a U.S. Marshal on his back trail, Marc Kannon crosses the border into Mexico, where his brother is serving under General Basada. He hopes the French - Mexican conflict will be a place to hide for a few months. Marc is sorely disillusioned to discover his brother is riding with a gang of outlaws. Worse, their next target is a town he had passed through on his way across the border. A chance encounter leads him to kill one of Basada's men. From that point on, he knows he has to do whatever he can to prevent the destruction of Rio Diablo. The fight will be to the death, with his only help being cripples, children and petticoats. But even a woman in a petticoat will fight to save her home and the lives of her family.