Although this was the fifth novel written and published in the series, it takes place near the end of the events of "The Lion, the Witch, and the Wardrobe" and features appearances by a few of the characters therein.
Young Shasta knew he was different than the other boys growing up in Calormen. He was resigned to his life until he overheard his guardian planning to sell him into slavery to a nobleman. When Shasta met the nobleman's horse Bree, he was startled to learn that Bree could talk. The horse was a captured beast from the land of Narnia, where many animals have the gift of speech. Together, the pair set out to escape to Narnia. Along the way, they met Aravis, a young aristocrat, who was also fleeing Calormen with a talking horse. The four travelers set out together, facing adventures and dangers in their exodus.
Lewis paints the Calormenes as evil or shallow and the Narnians as good, but the characters are not all black and white. The heroes have flaws that make them more real: Bree is far too vain for his own good and Aravis is a spoiled brat at the beginning of the story.
The only weakness in this book is the convenient wrap-up at the end in which everything is explained too quickly and with too many coincidences.
Despite this small drawback, this is an enjoyable book that fits in well with the Narnia saga.