Jim is planning on entering a dog sled race and with his wonderful lead dog Rex he is a sure bet to win the race. He needs the prize money so that he can take is ill pop Pete to California for the sake of his health. However Rex is poisoned by a competitor and is too ill to enter the race on Saturday. Sergeant Preston sells his lead dog, King to Jim for $1 for a a day so that Jim can still enter his team in the race.