Perelandra continues to follow the interplanetary adventures of Dr. Elwin Ransom, a well-meaning philologist. It continues the trend from the previous novel (Out of the Silent Planet) of using Lewis himself as a narrator for the beginning and ending, relating his experiences with Ransom, whom he portrays as being a real person. Ransom calls Lewis to his house to talk "business," and when Lewis is on the way, he feels severely tempted to go back and disbelieve Ransom's story about Malacandra. When he comes to Ransom's house, he discovers an ice-like coffin and the Oyarsa (angel guardian) of Mars in one of Ransom's rooms. Ransom returns and explains the situation: the doubts Lewis felt on the way were placed in his mind by evil eldila (angel spirits). Ransom has been called to travel to Perelandra (Venus) and prevent an attack on its inhabitants by the Earthly fallen Oyarsa (the "black archon"). He has appointed Lewis as the trustworthy man who should "package" him up before his departure and be present at his return sometime in the indeterminate future. Lewis does so, recruiting a doctor named Humphrey in the meantime. The next year, Ransom returns, and Lewis and Humphrey notice a physical improvement in his condition along with an injured heel. From here on, the majority of the novel is told from the perspective of Ransom, who details his journey and mission.
After a mind-bending journey through the celestial spheres (or something of the sort), Ransom lands on the planet Perelandra. The landscape of the beautiful planet is quite unlike that of Malacandra; it consists of almost entirely ocean, with large floating "mattresses," or "carpets," of vegetation that serve as dynamic islands. Ransom eventually pulls himself onto one of these, noting the dim light and bright colors of this new, stunning paradise. He falls asleep as night comes, pulling himself "inland" to the trees on the floating island.
The next day, Ransom discovers the "bubble trees," which grow and dispel bubbles of air and water that, when popped, emit a highly pleasurable sensation of seeing the world with great color, clarity, and hope. He also makes a new friend: a dog-sized red dragon who acts like a dog. Later in the day, he discovers several more types of life on the island, all of which converge on a single "carpet." He makes his way there and meets Tinidril, the Queen of Perelandra, a green but humanoid person who is strikingly beautiful and serene. She is like a child in her knowledge of evil and fallen things, but she is the one who imparts most of the wisdom to Ransom. She reveals that, after Jesus took human form on Earth, all created life will now take the human form in homage to him. Malacandra is an old world, but all new worlds (like Perelandra) will have humanoid inhabitants.
Ransom learns that the King and Queen are the only of their kind on the island, and are therefore the Venusian equivalents of Earth's Adam and Eve. He gradually comes to realize that the attack from Earth's "black archon" will be a temptation similar to that of the Garden of Eden, which, if successful, will disrupt this heavenly paradise and create a fallen world akin to Earth. Ransom and Tinidril go on for a few weeks, sometimes seeing each other and falling into dialogue, but spending much time enjoying creation on their own.
This world is disrupted when Dr. Weston, the villain from the first novel, arrives on another land mass. He immediately threatens Ransom with a revolver he brought from Earth, which, of course, Tinidril does not understand. After she leaves, the two men converse, and Ransom learns that Weston has embraced the spiritual realm, but something still seems off about him. He believes in a great Force, comprising both God and the Devil, that pushes Life along, and he believes that he has been chosen by this Force to do great things.
For a significant portion of the novel, Weston (whom Ransom suspects to be possessed by an evil spirit) tries to convince the Queen to spend a night on the solitary stationary land mass on the planet, The Fixed Land, which was expressly disallowed by God. Ransom and Weston debate extensively, but the demon's cunning is so strong that his arguments seem to be gaining the advantage. Ransom, counseled by a divine voice, resorts to a physical attack against the Tempter, causing him to flee and spark a long, drawn-out battle across the various landscapes of the planet, including the ocean and caverns below the planet's surface. Ransom ultimately triumphs over his foe, casting his body into the geothermal abyss. It is notable that Ransom emerges with a bite on his heel, evoking the prophecy in Genesis 3:15, which says that the savior will crush the serpent's (Devil's) head, and the serpent will bite his heel. This image solidifies the image of Ransom as the mortal agent of salvation for the planet.
Escaping from the caverns, Ransom celebrates with the beings of Perelandra. The Oyeresu of Malacandra and Perelandra come together and bestow guardianship of the planet to the King and Queen in a ritual known as "The Great Dance," which comes to light as the deepest truth of Life in the Field of Arbol.
Ransom is sent back to Earth in the manner he predicted, tasked with bringing Life to the evil of his own planet, setting up the third and final installment in the Space Trilogy, That Hideous Strength.
