In this installment of the Chronicles of Narnia, the children go back to the land a year after their first visit. They are surprised to find that, although only a year has passed on Earth, many hundreds of years have passed in Narnia, and almost everything is different. Most of the magic is gone out of the land--the talking animals, moving trees, dwarves, and other creatures are little more than memories now, and the land is ruled and dominated by a race of men. The men, incidentally, are skeptical in nature, and do all they can to oppress magic and the true history of Narnia.
The symbolism in this book is very vivid, and Lewis uses the plot very well to show the situation of much of modern society. The race of men (led by Caspian's uncle) refuse to believe in magic, and also don't believe in Aslan. Aslan is a Christ figure, so this unbelief in him is symbolic of twentieth-century skepticism. Many people today do not believe in miracles or anything that cannot be scientifically 'proven,' and a similar situation exists in Narnia, where men here the old stories of magic but many do not believe them. In an allegorical sense, then, this novel shows us the folly of skepticism, and the absurdity of believing in a world in which nothing wonderful can occur.
Like the rest of the Chronicles of Narnia, this book is a delightful children's story. But there is a deep theology at work here, and this is one of the qualities which makes it appealing to adults. I highly recommend this book, along with the rest of the Chronicles, to anyone interested either in fairy tales or in Christian allegory or theology.