The Silver Chair by C.S. Lewis

The Silver Chair by C.S. Lewis is an exciting fantasy advnture for middle grade readers and older. Eustace Scrubb and his schoolmate, Jill Pole find themselves in Narnia after running through brush to escape school bullies and finding a door open in the wall that borders their school's property.

Aslan wants them to help the Narnians find the lost Prince Rilian, son of Caspian the 10th. Despite several mistakes, the two friends manage to get going on their adventure. But will they be able to find the lost prince, or will they end up like all the other heroes who have tried, and just...mysteriously disappear?