After overcoming personal tragedy, widowed father and champion musher Leonhard 'Sepp' Seppala steps in the midst of a diphtheria outbreak in his small dock town of Nome, Alaska to safely deliver the anti-toxin to the hospital. With his own child's life on the line, Sepp battles the impossible, accompanied by his trusty pack of sled dogs. When a severe winter storm has made it impossible journey for planes, trains, or any form of transportation, Sepp and his dogs are able to get the anti-toxin to the children in need, just in the nick of time.