For some reason Goodreads has this book as #4 in the Chronicles of Narnia and it isn’t it’s #6, so I hope that can be corrected.
#4 = Prince Caspian.
Prince Caspian is in this book although he’s King Caspian X whose son Prince Rilian has disappeared.
Eustace Scrubb and Jill Pole escape from bullies at their Experiment House school through a mysteriously open door in a wall which leads to an open moor and a massive cliff and a very large lion called….Aslan.
Eustace jumps off a cliff and Jill is given some instructions by Aslan to find the missing Prince Rilian, the heir to Caspian’s throne. Jill and Eustace both end up in Narnia where their adventure begins. Jill doesn’t pass the instructions on to Eustace in time, but they do meet an owl called Glimfeather who transports them to a Parliament of Owls. Then they meet a marsh-wiggle called Puddleglum, who is brave and pessimistic in equal measures.
Jill, Eustace, and Puddleglum cross Ettinsmoor, avoid ending up in a pie in Harfang – the ruined city of the Giants, and finally come face to face with an evil witch who must be defeated if Prince Rilian is to be saved (Hint: This involves The Silver Chair of the title).
What happens next…? Well read the book, because it’s really good and recommended, and I’ll have to start at #1 and read them in the correct order.
Back in the real world at the very end of the book, there’s an inquiry into how the headmistress of The Experiment House was running her school. 10 people were expelled due to bullying. The Headmaster’s friends saw that she was no good at being a Headmaster, so they made her an inspector so she could interfere with other headmasters. When they found she wasn’t much good at that, they got her into Parliament where she lived happily ever after!