The Silver Chair

In The Silver Chair, Aslan calls Eustace back to Narnia together with his classmate Jill Pole. There they are given four signs to aid them in the search for Prince Rilian, Caspian's son, who disappeared after setting out ten years earlier to avenge his mother's death. 50 years have passed in Narnia and Caspian, who was barely an adult in The Voyage of the Dawn Treader, is now an old man, while Eustace is still a child. Eustace and Jill, with the help of Puddleglum the Marsh-wiggle, face danger and betrayal on their quest to find Rilian.