"The Silver Chair" is the fourth book in C.S. Lewis's Chronicles of Narnia series. It follows the adventures of Eustace Scrubb and his classmate Jill Pole as they are summoned to Narnia to rescue Prince Rilian, the son of King Caspian. The two children face various challenges and creatures while navigating the enchanted land. Throughout their journey, Eustace and Jill are guided by Aslan, the great lion, who provides them with important instructions. They encounter the Green Witch, who has cast a spell on Rilian, leading to a thrilling climax where they must confront her to save the prince and restore peace to Narnia.