In old California, as a favor to a mine owner friend, ranch hand Hopalong Cassidy, his sidekick, Lucky Jenkins, and other ranch hands escort a load of gold bullion safely to Crescent City. When they deliver the gold to Jane Travers, owner of the Crescent City Freight Company, she informs "Hoppy" that unidentified outlaws have burned several of her storehouses and have robbed her wagon train shipments. Although she has called for U.S. troopers to guard her next shipment, Hoppy agrees to ride along as extra insurance. Hoppy becomes suspicious of the troopers when they arrive because of their motley uniforms and behavior, and tells Jane that he and his men will not ride along with her after all. Instead, they locate the area where the outlaws have intercepted and killed the real troopers, and Hoppy then gallops to meet the wagon train, knowing that it must be in trouble. Hoppy and his men trick the outlaws, led by Jim Ferber, into believing that they are the real troopers, and the outlaws flee. Hoppy and his men then accompany a grateful Jane to Eldorado. There, Jane's companion, Diana Westcott, joyfully greets her uncle, Stephen Westcott. Westcott behaves strangely, however, and Hoppy suspects him of involvement with the outlaws. He and Lucky consult with governor Don Pedro, who informs them that he has called for state troopers to help quiet the uprising between local Mexican and American residents. A local monk indicates that the dissent is being fomented by a local rancher, Ed Martin. Lucky, who is enamored of Diana, leaks the news of the troopers to Westcott, who works with Martin and concocts a plan to take over the town. Westcott urges Don Pedro to throw a fiesta; however, Martin takes everyone hostage at the party and declares his sovereignty. Hoppy escapes with Diana and takes refuge in the home of a friend of Jane's grizzled foreman, California Jack. Disguised as the monk, Hoppy gains entry to visit the hostages and sneaks in guns under his robes. The tables turn on Martin when Hoppy and friends thwart their own execution and Martin is killed. Jane joins Hoppy and their men when they battle the rest of the outlaws being led by Westcott. Hoppy finally captures Westcott, and he and the rest of the outlaws are brought to justice. With peace restored to Eldorado, the wagon train heads home.