Hopalong Cassidy, Johnny Nelson and California, ranch hands at the Bar-20, agree to help out neighboring rancher Charles Grant by accompanying him and his wife and daughter, Jane and Susan, to Arabia to buy stallions for the cavalry. During a perilous trek across the Arabian desert, led by their Arabian guide Yussuf, Hoppy, Johnny and California come to the aid of a camel train that is being raided, which has the same destination as they do, the Sheik Suleiman's encampment. After Hoppy presents his commission and gifts from the Grants to the sheik, Suleiman, who refuses to sell any Arabian horses, presents two horses to Hoppy as a thank you for saving his camel train. When Hoppy returns to town, he discovers that naïve Susan has befriended a couple named Marie and Nicki Karitza, who claim to be brother and sister, and that while Nicki was out scouting horses with Charles, they were accosted and Charles was kidnapped. Hoppy insists on trying to find Jim before paying the $50,000 ransom. He returns to Sheik Suleiman's camp, where Suleiman informs him that his rival, Faran El Kader, is most likely responsible for the kidnapping. While Hoppy and friends head toward El Kader's camp, the Karitzas kidnap Susan, who has cabled the United States for the ransom money because she distrusts Hoppy. With the help of Yussuf, Hoppy frees Charles and Susan and remands El Kader, Nicki and Marie, who are actually a husband and wife team of con artists, to Suleiman's custody. El Kader's tribe launches an attack against Suleiman's camp, but Hoppy uses an old Apache trick to ambush El Kader's tribe. After Suleiman conquers El Kader in a sword fight, peace returns to the desert, and the cowboys and the Grants return home.