Sierra Sue is about a rural community facing a major problem. A weed capable of poisoning cattle and killing them is sweeping through the area, and nobody can control it. The local banker Stacy Bromfield (Frank Thomas) decides enough is enough and calls upon the government for help. In turn, the government sends out inspector Gene (Gene Autry) to figure out how to deal with the problem. Gene suggests killing the weed by spraying a certain chemical on it from an airplane, but the ranchers, headed by Smiley Burnette (Frog Millhouse) do not like the idea. They feel that burning the area will solve the problem in no time. Smiley and Gene want their idea to work so they receive credit for saving the day and impressing the girl Fay McKenzie (Sue Larrabee). Who will save the day and win the girl? Find out in this amusing early 1940s classic directed by William Morgan.