Caryl Foray is convinced that her boss, Enos Colvin, is planning to steal a fortune in securities from their company. She thwarts his scheme by mailing the bonds to her uncle, Jean Foray, in the mountains of Northwest Canada. She's hoping to gather more evidence against Colvin, but instead her actions lead to the murder of her uncle and the shooting of his dog, Rinty. The wounded dog crawls to the headquarters of the Royal Canadian Mounted Police, who soon discover the brutal crime scene at the fur trapper's cabin. The authorities must rely on Rinty, the sole witness, to lead them to the killers.
Rin Tin Tin Jr. stars as the canine hero in Caryl of the Mountains. He was the second in a long line of progeny sired by the original star of the silent screen, Rin Tin Tin. Coincidentally, Rinty's co- star, Ralph Bushman (credited here as Francis X. Bushman, Jr.) was also the son of a great silent film star.