Nome, Alaska, 1925. A diphtheria epidemic is sweeping through Nome, and 18 people have already gotten sick. One person is the owner of Jenna, a dog that Balto has a crush on, and who also has a crush on Balto. The town's doctor sends for more diphtheria antitoxin, which Nome is out of. A dog team is sent to Nenana to pick up the antitoxin, but on the way back, there is an accident, and the musher is knocked out. When the team doesn't arrive, Balto goes to help them out. He is, of course, bullied by Steele, his rival. Balto ends up leading the team, and on the way back, has an accident, but proves himself by bringing the antitoxin safely to Nome, and becomes a hero.
Steele, on the other hand, gets rejected and is despised by the other dogs..