The two youngest of the four children – Edmund and Lucy – are staying with a nasty young relative, Eustace Scrubb over the holidays. The three of them are drawn into Narnia together through a painting of a ship at sea and find themselves on a real ship in Narnia with their old friend Caspian from the previous story. He is in the midst of a great sea voyage through many lands beyond Narnia, searching for great men of Narnia the previous king had sent into exile.

The book is strongly reminiscent of the great Greek epic, Homer's Odyssey while Christian themes abound, such as: repentance, our need for supernatural help in fighting our vices, the horrors of slavery, the dangers of magic, etc.

Here is a small sampling (the first few paragraphs of the book):

There was a boy called Eustace Clarence Scrubb, and he almost deserved it. His parents called him Eustace Clarence and masters called him Scrubb. I can't tell you how his friends spoke to him, for he had none. He didn't call his Father and Mother "Father" and "Mother," but Harold and Alberta. They were very up-to-date and advanced people. They were vegetarians, non-smokers and teetotalers and wore a special kind of underclothes. In their house there was very little furniture and very few clothes on beds and the windows were always open.

Eustace Clarence liked animals, especially bettles, if they were dead and pinned on a card. He liked books if they were books of information and had pictures of grain elevators or of fat foreign children doing exercises in model schools.

Eustace Clarence disliked his cousins the four Pevensies, Peter, Susan, Edmund and Lucy. But he was quite glad when he heard that Edmund and Lucy were coming to stay. For deep down inside him he liked bossing and bullying; and, though he was a puny little person who couldn't have stood up even to Lucy, let alone Edmund, in a fight, he knew that there are dozens of ways to give people a bad time if you are in your own home and they are only visitors.