After the Bar-20 cattle are rustled, foreman Hopalong Cassidy and his ranch hands, Lucky Jenkins and California, are sent to recover the stolen herd. In nearby Gunsight, newspaper publisher Jim Stuart and his daughter Joan are sure the run of trouble is saloon owner Belle Langtry's responsibility, so Jim writes an editorial against Belle. Belle's right-hand man, Steve Fraser, meanwhile, gets older miner Pete drunk so he will reveal the site of his recent claim, which Belle and Steve plan to jump. Steve and his thugs succeed in obtaining Pete's papers and then get rid of him. Soon after, Hoppy meets Belle as he is traveling to Gunsight and tries to rescue her because her horse appears to be out of control. However, Belle is always in control of her horse and every situation, and flirts with Hoppy. As Hoppy, Lucky and California arrive in town, they notice a violent fight occurring in the newspaper office. Steve and his men are destroying the office in retaliation for the editorial, so Hoppy defends the Stuarts and forces Steve and his gang to leave at gunpoint. While Lucky and California help Joan clean up, Hoppy introduces himself to Jim, and accepts his offer to become the town's new sheriff. At Belle's saloon, Steve learns about a huge cattle drive which he intends to rustle, and when Hoppy comes into the saloon to announce publicly his intention to clean up the town, Belle is surprised to find out that she and her new friend are on opposite sides of the law. Steve worries that Belle will be swayed by her attraction to Hoppy, but she assures him that she cannot be moved. Hoppy later learns that Jim and his friends hold Belle liable for Pete's death because she filed his claim, and Hoppy surmises that Belle uses her position at the saloon to gather valuable information. Hoppy plans with Jim's rancher friends, Reed Jackson and Tom Wilson, to entrap the gang with a fake shipment of cash. Steve and his gang are surprised when Hoppy and friends open fire on them as they steal the money from the stagecoach. In the ensuing gunfight, two of Steve's men are killed and Ed Stark, one of the gang, is arrested, while California receives a minor head wound. Later, Belle attempts to seduce Hoppy, but he is resistant to her charms. California lets Ed escape from jail and sees that he is headed north. They find the hideout by following Ed's trail and capture most of the gang and recover their stolen cattle. One gang member, Red, escapes and reports to Steve, who accuses Belle of selling out to Hoppy. Steve plants his men around town to prepare for a gun battle, and holds Belle and Joan, who was captured trying to warn Hoppy, captive. However, Joan succeeds in firing a warning shot, and Hoppy becomes determined to "clean out" the bar that night. Hoppy calls a cease fire when Steve threatens to kill Joan, but Belle, outraged by Steve's rough treatment of Joan, helps her escape, and is shot by Steve in the process. Hoppy then breaks into Steve's room, and in the ensuing struggle, Steve falls from a window to his death. While Hoppy nurses a gunshot wound on his shoulder, Belle, recovered from her injury, parts friends with him as she is taken to prison.