The Space Trilogy: Out of the Silent Plant; Perelandra; That Hideous Strength

Complete in three volumes. The Space Trilogy recounts the adventures of Elwin Ransom (in part based upon Lewis's good friend J.R.R. Tolkien), with interesting religious themes expanded out into a setting that includes Mars, Venus, and Earth. In Lewis's universe, Earth is the 'silent planet', cut off from the rest of the solar system because it is viewed as a fallen civilization.