Early in the book a man named Ransom is travelling from town to town in search of lodging. Ransom is a professor of philology, an academic discipline where words, phonetics, and other linguistic constructs are observed. Ransom comes across three men fighting, and through a twist of fate is kidnapped by two professors who are going to explore a planet called Malacandra.
After their touch down in Malacandra, Ransom is blown away by the vast differences between Earth and Malacandra. The three men are confronted by giant ghost-like creatures. Ransom runs for his life, and becomes stranded alone on the strange planet. This is the story of his adventures and exploration of the planet Malacandra.
The main reason I give this four stars is probably because I haven't read the rest of the trilogy yet, but the story is very exciting once the plot is set up about a third through the book. I can't tell you more than what is above for concern I might give away something.
Unfortunately, some of my favorite parts of the book fall into that category of stuff I can't give away. However, what I can say is this. Science fiction often encourages our philosophical and theological imagination. The effectiveness with which Lewis does this is significant. I highly recommend this book.