Bronco wins 1000 head of cattle in a poker game. However, when he tries to bring them to market, he runs into one rancher who charges him outrageous fees for grazing rights and another who won't let Bronco cross his property to take the cattle to market.
Bronco is working undercover with the Army to seek out the identity of a former Confederate guerrilla who is still at large and find out what has happened to a large cache of stolen Union gold. He becomes involved with a beautiful woman card dealer who could be an escaped Confederate spy. Bronco wins her trust and uses it to infiltrate their ring and get close to the truth.
Bronco is traveling across the Rio Grande River, which separates the US from Mexico, when he sees a woman and a young boy who are crossing from the Mexican side being shot at. He helps them across and finds shelter at the cabin of an old widow. He is then astonished to learn that the boy is the son of the late Emperor of Mexico.