The Space Trilogy is CS Lewis's allegorical statement of theology and philosophy. Lewis was one of the most prominent Christian apologists of his time, but he always felt there was an audience he couldn't reach. This was his solution, and we are left with a masterpiece both in the world of fiction and the world of theology.
The hero of the books is Dr. Ransom, a philologist who is a good man, though not exceptionally heroic at first. The first book finds him captured and whisked off to Mars, where he encounters a society much more morally advanced than our own, and learns that the corruption of our planet is due to an evil influence (which we would call Satan). These higher creatures cannot grasp the concepts of war, murder, or any vice.
The second book finds Ransom transported to Perelandra, also known as Venus. This is Lewis's allegory of the garden of Eden, and here he encounters an unfallen woman who is being tempted into doing the forbidden. Here Ransom learns of the nature of sin, and of the temptation that (Lewis says) befell the parents of our own race.
The final book is quite different from the other two, and Ransom, this time on Earth, is battling an evil organization which is bent on penetrating the mysteries of the universe and purifying the human race. Ransom and his followers are aided by a power that has long slept, and together they battle the power of science gone haywire. We see, through their eyes, the evils of society and of so-called 'higher thought.'
There are many lessons to be learned from this wonderful trilogy, but there is also a remarkable story to be told. If you're a fan of fantasy and science fiction, a reader of Christian and theological works, or both, you will greatly enjoy the Space Trilogy.