What is the main event in the story horse and this boy?

In "The Horse and His Boy" by C.S. Lewis, the main event revolves around the journey of a young boy named Shasta and a talking horse named Bree as they escape from the kingdom of Calormen to the freedom of Archenland and Narnia. Along the way, they encounter various challenges, meet other characters such as Aravis and her horse Hwin, and discover their true identities. The story culminates in their heroic involvement in thwarting a plot against Archenland, revealing themes of friendship, courage, and self-discovery. Ultimately, Shasta learns about his true heritage and his connection to Narnia.