First published in 1978, A Swiftly Tilting Planet is the third book in the science fiction Time Quintet by Madeleine L'Engle. The first book in the series is A Wrinkle in Time. A Swiftly Tilting Planet begins ten years after the last events in A Wind in the Door, and involves the same characters. Meg and Calvin are married, and Charles Wallace is told by a unicorn that he must prevent a nuclear war by time travel. The book incorporates both science fiction and fantasy elements, including mythical species and advanced machinery.
Madeleine L'Engle was an American writer that was best known for her A Wrinkle in Time series. Many of her fiction, non-fiction, and poetic works involve aspects of her strong Christian faith synthesized with modern technology. L'Engle struggled financially as an author for the much of her career, and only in her 40's did she gain recognition for her works. She has received numerous awards for her literature including the Regina Medal and the Kerlan Award.