 The 23rd (and next to last) Mascot sound serial, with the first two billed names above the title and the cast frame sheets those of Rex, the King of Wild Horses, and Rinty (Rin-Tin-Tin, Jr.), thereby making the cast order for the human players two less than shown (Kane Richmond is 3rd billed in reality and not first, opens on the island of Sujan, off the coast or eastern Africa, where guarded by jungles, roving beasts and the Sacred Guard, nestles a shrine to a sacred horse, the black Arabian Rex, the God-Horse of Sujan. High Priest Tanaga (Mischa Auer) innocently allows to Americans, Mitchell (Al Bridges) and Wheeler (Wheeler Oakman) see the sacred stallion and, with the aid of Martin (Charles King), they steal the horse and bring it to the United States, where they sell it to Crawford (Harry Woods), a wealthy, greedy polo-playing rancher. Crawford attempts to train Rex as a polo horse, but royal Rex (King of the Wild Horses) isn t having any of that, escapes and takes to the open road or, in this case, range. There he teams up with the vagabond dog, Rinty (Rin-Tin-Tin, Jr), and they avoid capture by Crawford and his henchmen Jones (Edmund Cobb), Anderson (George Chesebro) and McDonald (Jack Rockwell.) Their activities attract the attention of polo-player Frank Bradley (Kane Richmond), who befriends the animals and takes them both back to the island of Sujan. Crawford follows and convinces the natives to turn against their God-Horse, and Rex is about to be burned as a sacrifice.