Hopalong Cassidy goes undercover as a hypochondriac, bumbling city man named William "Harold" Cassidy, to help a sheriff find the murderer of Ann Marsh's husband, who was killed and robbed of $30,000 cash he had just made from selling his cattle to Monte Keller, a casino owner. Following the advice of the express agent on whose stagecoach John Marsh was killed, Ann returns to Silver City with her daughter Dorrie and opens a dude ranch while awaiting the arrival of Hopalong. Hopalong arrives with the other guests, and his demeanor seems unpromising to Ann. She feels threatened by Steve Dorman, whom Keller insisted work for Ann. Hopalong's sidekicks, Windy Halliday and Lucky Jenkins, hire on at Ann's ranch as part of Hopalong's plan. Lucky takes an interest in Dorrie, who is also frightened by Steve. While gambling at Keller's casino at night, Hoppy finds out that the serial numbers on several hundreds he won match those that Ann remembered as being part of the stolen $30,000. He confronts Steve, but Steve escapes. A gunfight ensues in which Hopalong is forced to kill Steve, after which Ann and the guests find out Hopalong's true identity. He sends Lucky to forewarn the Silver City patrol to expect Keller's men, who will attempt to rob the stagecoach. He then arranges with Ann to pretend to make Keller her partner in a scheme to rob Hopalong, in disguise, of his bankroll. Hopalong wins back $30,000 in poker from Keller and boards the stagecoach. Meanwhile, one of Keller's men reports back to him of Steve's murder and Hopalong's true identity. They pursue the stagecoach and are met by the patrol. Hopalong finally wrestles Keller off his horse and shoots him in self-defense. Hopalong resumes his normal guise, and he, Windy and Lucky leave the ranch, leaving a few broken hearts behind.