Rin-Tin-Tin is saved from the beatings of a trapper by Ed Nolan, a shiftless trapper himself, and 'Rinty" follows Nolan home to his cabin but refuses to enter. Nolan takes him to the home of Mary Mallory, the girl he has failed to win as his wife because of his ways, and in their mutual love of 'Rinty," a new understanding is born and Nolan goes to work. When Mary's baby sister gets sick, Mary thinks 'Rinty' must have turned on her because of the blood on his jaws and Noland decides to shoot him, but 'Rinty' runs away. The little girl becomes critically ill and Mary starts for the doctor with her through a blinding snow storm. The dog-team capsizes the sled and runs away. The faithful 'Rinty,' who has been following them, takes a note from Mary to Nolan. The latter comes to their rescue, and the doctor tells them the baby sister was bitten by a wolf, and the blood on 'Rinty' came from his fight against the wolf. The little sister will get well, and 'Rinty' accepts the apologies from Mary and Nolan.