The Silver Chair
While running from bullies at school Eustace and Jill find themselves in Narnia where Aslan gives them a task to perform. They are told to find Prince Rillian, son of King Caspian, and return him to his father. While Caspian was a young man the last time Eustace saw him in The Voyage of the Dawn Treader, he is now an old man, heartbroken that his son is gone. The two children and a gloomy marshwiggle called Puddleglum search for the prince avoiding great dangers from Giants, earthmen, and a deadly serpent. They find the Prince and free him from a spell, but when they return, Caspian has just died. Aslan interrupts their sadness and takes them to see Caspian, who is rejuvenated as a young man in Aslan's country with a drop of Aslan's blood brought force by a thorn. In the world of Narnia Caspian is dead, but in Aslan's land he lives forevermore. Eustace and Jill are returned to their school where they drive off the bullies and make things right once again. 
A film adaptation of The Silver Chair is in the works. However, on January 13, 2015, it was announced that the film would be a partial reboot, not featuring any of the actors from the previous three films. 
- Companion to Narnia, Harper SanFrancisco, 1980.
- The Silver Chair by C.S. Lewis, Macmillan Publishers, 1953.