A loyal German Shepherd dog follows his master to the French front in World War One.

Eddie Phillips works for his father, an oilman searching for deposits in the north woods. A puppy intended for Eddie falls out of the truck that's transporting him and is stranded in the forest, but the pup learns to survive on his own and soon becomes master of his domain. A year or so later Eddie and another dog, White Fawn, happen to be camping near property owned by pretty young Betty Francisco when swindler Jim Mason discovers oil deposits on Betty's land the tries to swindle her out of them, but the heroic dog, now named Thunder, determines to stop Mason and Eddie helps him, not knowing that Thunder is the dog originally meant for him.

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.

New Yorker David Kingston, a university student involved in the study of mine engineering, is falsely accused of theft and expelled from school. David's mother soon dies of grief, and he decides to end it all by jumping in the river. David is deterred from suicide, however, when he adopts a stray pup, which he names "Thunder." The dog later finds a map indicating the location of a gold mine, and David heads west to Northern California.