In the Alaskan village of Topek, the dog Firefly grieves when her master dies and is taken in by visiting authoress Jean Williams. Though Jean loves the rough Alaskan wilderness, she cannot understand the seemingly cruel ways of its men, especially trapper Gaston Rogers, who tries to convince her to leave the village. After the entire population leaves because they are unable to obtain the reindeer meat they need to survive until spring, Jean agrees to go, but wants to travel to Nenana to see the annual ice-breaking instead of taking the safer route to Fairbanks with Gaston. Gaston travels with her, however, and they become attracted to each other, although Jean still finds Gaston's cruel ways abhorent. Along the trail, Firefly is fed by Jean, even though they are short on rations, and Gaston becomes angry when Swift Lightning, a wild dog who earlier had caused him to lose some of his furs, courts Firefly. When an avalanche almost kills them, they are dug out by Swift Ligtning, but Gaston still refuses to give the dog food, angering Jean. Meanwhile, in Nenana, Hugo Henderson, who is in love with Jean, waits for the ice to break and joins in the betting pool, which has grown to $85,000. Jean writes a diary about the journey and notes that the dogs are still trailing, though they are starving. At the same time that the betting pool is won by local fisherman Joe, Gaston and Jean find themselves trapped on a melting ice floe. After admitting that she has caused their situation to become desperate, Jean realizes that she is in love with Gaston. In love with her as well, he decides to kill Firefly for food for her, but she stops him just as Swift Lightning starts to attack, and says that she can never forgive his intended cruelty to the dog. They soon find refuge at a deserted cabin, and after a trapper has reported finding their abandoned sled, Hugo and some men from Nenana go looking for them. Hugo and his dog Buck, a pedigree, arrive at the cabin just as Gaston grabs Jean and kisses her, after which the men fight. Jean stops Gaston from killing Hugo, and because he thinks that Jean really loves Hugo, Gaston leaves. When a blizzard erupts, Swift Lightning is trapped by a falling tree and Firefly, sensing her mate's danger, goes after him. Jean follows, and finding Gaston desperately helping to free Swift Lightning, she realizes that she has misjudged him. After they all return to the cabin, Jean tells Hugo that she plans to stay with Gaston, and Firefly lets Buck know that she prefers Swift Lightning. The next spring, Firefly and Swift Lightning have a litter of puppies and Gaston and Jean are happy together.