The Brave Journey — Jefferson Knapp

After his beloved dog, Pugsly, dies, 12-year-old Benjamin Biggs stumbles upon a secret underground kingdom of misfit animals across the road from his country home. Wearing his dog's collar as a bracelet, he finds he is able to talk to the animals, learning that their king, Pugsly, was assassinated by the giant, mysterious python, Farangis. With news of Farangis soon returning to kill the rest of them, Benjamin agrees to lead a small band of quirky animals on a long and dangerous journey to save the kingdom. Through discovering the secret life his dog lived, Benjamin learns that loyalty and friendship can ultimately involve sacrifice.