The Horse and His boy by C.S. Lewis

The Horse and His Boy, by C.S. Lewis, is the only story that takes place in Narnia where the protagonists are native born Narnians (well, Aravis is Calormen, but still in that world). Shasta, a boy whom we would call Caucasian, is raised in a land by a Calormen man that we would call Middle Eastern. He calls the man "Father", but wonders sometimes why they look so different.

One night, he gets a shock. Overhearing Arsheesh (his supposed father) talking to a rich man, he discovers that Arsheesh is not his father, and is willing to sell him to the rich man. Uncertain what to do, he is talking to himself about the problem, when the rich man's horse speaks up. It turns out that the horse, Bree, was born a Narnian talking horse, and was kidnapped as a foal. Together, the two plan their escape. A few days later, they meet Aravis and Hwin, a Calormen girl about Shasta's age, and a talking Narnian mare with a similar story to Bree's. The four decide to escape together. During the course of their escape they meet most of the Pevenseses from the other books, and of course Aslan. But with Rabadash the crown prince not far behind them, will they make it to Narnia safe? Read the book (or listen to the audio like I did) and find out!