A Swiftly Tilting Planet is the third book in Madeleine L'Engle's Time Quintet, which follows the adventures of the Murray family. Ten years have passed since book 2's events and Meg is now married to Calvin and expecting their first child. Calvin's mother Branwen visits the Murray family for Thanksgiving, which is interrupted when the US president phones Meg's scientist father to inform him of an impending nuclear war threatened by the South American dictator "Mad Dog" Branzillo.
As in the previous two novels, the family seeks to avert the coming disaster and is assisted by an angelic figure - a winged unicorn named Gaudior in this story. But, while "A Wrinkle in Time" and "A Wind in the Door" dealt with time as a separate dimension, rather than a forward-only vector, this book introduces actual time travel. Meg's genius brother Charles Wallace and Gaudior travel back in time to discover the origins of Mad Dog and attempt to alter history and avert war.
This is a clever adventure story that kept me enthralled. It was nice to see Charles Wallace take a more active role, rather than being the child who must be rescued. Meg remains in the present but communicates telepathically with her brother across the centuries. The story spans hundreds of years, but is tied together by the familial relationship between the characters encountered by Gaudior and CW. The only weakness was the transparent name games that the author played, which were too easy for the reader to figure out, even though it took genius Charles Wallace more than half the book to get it.
I look forward to volume 4.