O vencedor do Oscar Charlton Heston interpreta John Thornton, um homem destemido que busca mais do que ouro; ele quer fazer o que é certo. Thornton trabalha para o correio dos EUA e é a única pessoa ousada e inteligente o suficiente para descobrir como viajar as mortais 600 milhas de Skagway para Dawson, no Alasca, no inverno gelado. Seu incrivel cachorro Buck está sempre ao seu lado e é parte da explicação de como Thornton sobrevive.
Adventuring author Jean Williams is living in the wilds of Alaska alongside the Eskimo people gathering material for her novel. She befriends several animals who become her loyal friends such as a pair of bear cubs whose mother has been killed by hunter Gaston Rogers, a talking raven and the bereaved collie Firefly who will not leave the grave of her master, a game warden killed in the line of duty. The community is imperiled by a pack of wolves and wild dogs, led by a wild dog called Swift Lightning, who are killing all the reindeer. With the supply of fresh meat gone, the Eskimos are migrating to lands with more food. Hunter Gaston agrees to take Jean to Nenana, Alaska, along with his furs by dog sled. Jean, who despises Gaston as being more savage and blood thirsty than the four-legged predators, is followed by her loyal animals.
In this western, the Three Mesquiteers must find a killer and his band after they murder an official from the State Agricultural Service who had come to investigate an outbreak of hoof and mouth disease. The killer is fearful that the official would quarantine his entire herd. Unfortunately for the foolish rancher, if the herd is not isolated, all of his cows and those of his neighbors will die anyway. The heroes are assisted by Buck the clever Great Dane.
Jack Thornton has trouble winning enough at cards for the stake he needs to get to the Alaska gold fields. His luck changes when he pays $250 for Buck, a sled dog that is part wolf to keep him from being shot by an arrogant Englishman also headed for the Yukon. En route to the Yukon with Shorty Houlihan -- who spent time in jail for opening someone else's letter with a map of where gold is to be found -- Jack rescues a woman whose husband was the addressee of that letter. Buck helps Jack win a $1,000 bet to get the supplies he needs. And when Jack and Claire Blake pet Buck one night, fingers touch.
