Robbers kill Pop Warner, the driver of the Cloverdale stage, making off with the large payroll he was carrying. The only witness to the murder is Pop's trusty dog, Rannah. Insurance agent Ted Sanders is called in to investigate the crime and he's soon joined by Deputy Barlow. After several attempts are made on Rannah's life, Sanders encounters another man who also claims to be Deputy Barlow. Confronted with this new mystery, Sanders must rely on Rannah's keen sense of sight and smell to uncover the conspiracy.
The canine actor in Vengeance of Rannah, Rin Tin Tin Jr., was sired by the original silent screen star, Rin Tin Tin, who had been discovered in France by an American soldier fighting in the trenches during World War I. The Rin Tin Tin dynasty, which continues to this day, produced offspring who delighted audiences young and old for decades, starring in film, radio and television.