It was February 1925 in the Alaskan wilderness. One wrong step could mean sudden death for musher Gunnar Kaasen and his lead sled dog, Balto. The temperature had dropped to -50°F. Fierce winds roared as snow pounded the sled. The blinding blizzard made it impossible to see. Waiting for the weather to change, however, wasn't an option. Fifty miles away in Nome, Alaska, dozens of the town's children were sick with diphtheria and near death. Gunnar...