At the beginning of the book when Faolan's mom had her cubs, there was one cub that couldn't move on with the rest, and it was Faolan. He had a form of deformity. The pack rule is if one of your vubs are hurt or unable to continue they have to stay behind. So Faolan's mom left him in a river on an ice block to die because he couldn't continue with the pack.
In the middle of the story Faolan meets a grizzly bear named Thunderheart. Faolan and Thunderheart become friends and work together to survive. They look out for each other like when winter came Thunderheart kept warning Faolan to sleep. They would hunt with each other to make sure the other is safe.
Faolan makes it back with his pack and proves them that he with his form of disability. The leaders enlist another gnaw wolf to rewrite their history so it explains who Faolan is and how he has returned. They invite him to join the MacDuncan clan as a low ranking gnaw wolf, and he accepts.