The next book in the Narnia series is The Horse and His Boy, but Andrew Adamson decided it would be best to jump straight to the fourth book, Prince Caspian, in interest of time. The struggle with a franchise like Narnia is how it leans on its young cast, who were growing rapidly as the film was being developed. In 2008, Prince Caspian was released to milder performance, at $419 million worldwide, with comparable quality to the first. Two years later, the fifth book was adapted with The Voyage of the Dawn Treader which made $415 million worldwide. All three Narnia movies are available to stream on Disney+, which you can sign up for using this link.