Weston and Devine are taken to a guest house while Ransom stays to talk with Oyarsa. A mysterious narrator (later shown to be Lewis himself) explains that the contents of this conversation are not meant for this book. Oyarsa does ask Ransom if he will go back to Earth or stay on Malacandra. After much thought, Ransom decides he must remain loyal to his own planet. Oyarsa approves and informs Ransom that he will send eldila to protect Ransom in space. Oyarsa lets Ransom go with a warning not to be fearful and to listen to the will of Maleldil for his life. According to Oyarsa, this heavenly year was prophesized to be a year of great change, and could mean that Ransom’s return to Thulcandra may open this silent planet.
The narrator leaves some things to the reader’s imagination, allowing Ransom’s full spiritual conversion to remain a personal decision between him and Oyarsa. Lewis hints that one’s religious beliefs can and should remain a personal matter between a person and God. Finally, Oyarsa cautions Ransom against that fear which makes him choose the wrong path, and he also gives Ransom a mission: to spread the word of Maleldil. Rather than a vague walking-tour, Ransom now has a more urgent purpose on Earth.
The next day, the three humans embark for their dangerous journey. Weston warns them all not to move to conserve oxygen, while Devine seems to have given up entirely and devotes himself to drinking. The spaceship takes off, and the handramits in which Ransom lived grow smaller. Ransom fears that all he has learned on the trip will disappear as fantastic mythology when he returns to his mundane life on Earth.
Lewis now includes another aspect of the average science fiction novel, adding a race against the clock journey. In this return to the genre, Ransom also fears a loss of the spiritual knowledge that he gained on Malacandra. Just as Ransom hopes to carry the lessons of Malacandra into his everyday life, Lewis hopes that his readers will take the events of his book with them into their lives.
As the spaceship continues to blast away from Malacandra, Ransom is overcome by fear at the sight of black space swallowing the bright disc of the planet. Soon Malacandra hangs in the distance, a small red dot that Ransom can only call Mars – not the world he has come to know. Ransom spends the first few days of his journey writing recollections of his time on Malacandra, desperately trying to hold on to this experience so he can share it with others on Earth.
The space ship journey begins Ransom’s return to the “real world.” His fear about space and the unknown creep back in, even though Ransom tries desperately to hold on to the lessons of acceptance and faith that he learned on Malacandra. With the experience fresh in his mind, Ransom is totally committed to his mission to share this news with others.
As the days of oxygen tick down, Ransom hopes that they will be killed by the disappearance of the spaceship and left to float free in the vitality and light of heaven, rather than suffocating in this small iron box. He finds it hard to trust that Oyarsa’s eldila are protecting him, unable to sense them in any way or believe that these heavenly beings care about the life of one insignificant man.
Ransom hopes to be killed floating free in the wonder of space, going through some version of Heaven. As suffering and everyday pain returns to his life, he finds it harder to keep his faith in Oyarsa and the eldila, as Lewis points out that many people lose their belief during the trials and tribulations of daily life.
Over the next weeks, Ransom realizes that Weston is bringing them far closer to the sun than they had come on the trip out to Malacandra, hoping to cut off some time in their voyage. After a few hours at the hottest temperatures the human body can survive, the spaceship mercifully makes it past the midpoint of the sun and the heat begins to lessen.
Weston, Devine, and Ransom suffer, but they survive. Lewis hints that the eldila do have a hand in keeping the humans alive through this incident. In Lewis’s conception, God promises to help his people, not keep them totally comfortable.
Weston, Devine, and Ransom all hope wildly that they will make it to Earth, doing little but staring at the shiny dot of the planet out the window. On the 87th day, Ransom sees the awful sign that the moon is directly in their pathway and will prevent them from any chance of landing in time before the ship disappears. Devine is forced to change course, bringing the space ship farther from Earth with only two days of air to go.
Weston, Devine, and Ransom are forced to think of nothing but survival, like animals. Through their own power, it is impossible for the humans to get home, since Weston’s calculations didn’t account for the moon. Lewis points out that humans need the assistance of larger powers in the universe.
Ransom goes to his bedroom to prepare himself for this inevitable death, and surprisingly falls asleep. When he awakes, he hears rain on the roof of the spaceship. Ransom realizes that they somehow managed to land on Earth. Weston and Devine are nowhere to be found as Ransom clambers out of the ship and soaks in the wonderful smell of new rain. He walks away from the ship, noticing a bright flash of light after about half an hour—meaning the spaceship has disappeared. Ransom reaches a bar, hears voices speaking English inside, goes in, and orders a pint.
Ransom, following the example of the hrossa, hopes to make peace with death rather than fearing it. Yet, through no power that Ransom understands, the space ship makes it to Earth. Lewis hints that the eldila really did have a hand in saving the space ship, though none of the humans saw them. Ransom now suddenly returns to “normal” life, getting a pint at a bar as if this were an average day.