The Silent Avenger (1927)

Stanley Gilmore, the son of a railroad president, atones for a series of wild escapades by traveling to Tennessee to secure a right-of-way through the property of farmer Dave Wade. Accompanied by his dog, Thunder, Stanley meets with Dave and initiates a friendship with the farmer's daughter, Patsy. Stanley's arrival is noted by Joe Sneed, a henchman of Bill Garton, engineer for a rival railroad. When the dog thwarts Bill's attempt to steal important documents from Stanley, the engineer informs the corrupt sheriff. Later, Thunder battles a bear in defense of Little Bud Wade, then saves the boy from drowning at the hands of Joe and the sheriff. While sending his father a telegram, Stanley is kidnapped, but Thunder rescues his master, flags down a train, and drives the villains to their death. Stanley finds happiness with Patsy, and his father acquires the right-of-way.