When Bill Cassidy returns to the Bar-20 ranch from Texas, his friend Buck Peters hires him to be the line foreman. The neighboring ranch owner, Jim Meeker, has been sending his cattle onto Bar-20 land for water against Buck's wishes. Jim's foreman Jack Anthony, working with cattle rustlers, fuels this argument over water rights to obscure their operations by killing Meeker's cowhands and stealing from both herds. Johnny Nelson, a young cowhand at the Bar-20, falls in love with Jim's daughter Mary and resents Bill's arrival at the ranch because Uncle Ben, Buck and Red Connors practically revere him, and because Bill gives Johnny fatherly advice. The feud between the ranches heats up, and Bill suffers a gunshot wound in the leg while trying to rescue Johnny from a lynch mob. Bill insists he can "hop-a-long" alright with his injured leg, and resolves to discover who is rustling the herds and instigating the feud between the ranches. When Ben finds a hide whose brand has been altered from Bar-20, Bill realizes both the Bar-20 brands and Jim's brands could be changed to read as the same brand. With this evidence, he and Jim ally the two ranches to work against the rustlers. Anthony kills Ben after he discovers the rustlers' hideout in Thunder Mesa, but Ben scrawls the location in the dust before he dies. Bill finds Ben and the message, and infuriated by Ben's death, rounds up every available man and captures the hideout and the rustlers. Too cowardly to fight, Anthony tries to escape, but falls over a cliff to his death. Johnny has gained new respect for Bill and with peace restored, he leaves Mary behind to join Bill and Red, who plan to buy their own ranch in Wyoming.