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 On the way to the mine, David stops at a sheep ranch, discovering there that the young daughter of the rancher is missing. Thunder soon finds the child, and David rescues her with the help of Randall Phillips, a mining engineer. Phillips later learns of David's map and attempts to kill him. Thunder is then falsely accused of killing sheep, being narrowly saved from the sheriff's posse by the little girl he rescued. David and the dog find the mine and enter its shaft, not knowing that Phillips has sabotaged it with dynamite. Phillips sets off the charge and is himself killed in the explosion; Thunder rescues David. The blast exposes a vein of gold, and David asks the oldest daughter of the sheep rancher, Marjorie, to marry him.—AFI