"Hopalong" Cassidy, "Lucky" Jenkins and "Speedy" are driving a herd of Bar-20 mustangs to Bluesky, to be delivered to Jeff Chapman, operator of a stagecoach line. They come upon a stagecoach, which has just been looted of silver bullion by "Smiley" and his singing outlaws. The Bar-20 men give first aid to Jeff, who was shot during the robbery, and "Lucky" drives the stagecoach to town. There, "Lucky" is hard smitten by Jeff's daughter, Shirley, but she is in love with Neal Holt, who also has designs on her father's mail-carrying contract. Holt's foreman, "Twister" Maxwell, secretly works with "Smiley" and his gang, tipping them off on gold and silver shipments. Hold and Cassidy get into an argument over the merits of the Bar-20 mustangs versus Holt's pure-bred Morgans and the end result is a match race, with the stage contract as the stake.