Meg Murry-O'Keefe, married to Calvin (no surprise) and expecting her first child, is home with the rest of the Murrys for Thanksgiving. Calvin is away in London giving a groundbreaking paper to a major conference, and so isn't present when Meg's father gets a disturbing call from the President of the United States. Mad Dog Branzillo, the military dictator of a South American republic is doing more than sabre-rattling with his nuclear weapons, and the President is not hopeful about the prospects for avoiding all-out nuclear war. The world could well end within twenty-four hours unless this very unreasonable despot is made to see reason.
Calvin's mother unexpectedly provides the family with a clue, however. It seems that Branzillo may be a very distant relation of the family. Fifteen year old Charles Wallace pounces on this very small hope and, with the help of a unicorn named Gaudior, kythes backward in time and experiences the joys and sorrows of the O'Keefe's ancient ancestors through their eyes. The story of the extensive family that eventually produces the insane Branzillo is explored, and Charles Wallace tries to subtly alter the 'might have beens' in the hopes of bringing about a better present. Can he do it? He has the help of Gaudior, and Meg Murry provides moral support via kythe, but opposing Charles Wallace are the Echthroi, who would be quite happy to see the Earth vanish in a mass of mushroom clouds.
A Swiftly Tilting Planet has its foot in both the Time Quartet and the O'Keefe family series of novels, and not just because Meg is pregnant with Polyhymnia O'Keefe. On the Time Quartet side, it features Charles Wallace kything and travelling back through time in order to save the world. On the O'Keefe family side, we are presented with a far more complex story about human interrelationships. The drama of the family that produces the insane Branzillo is told in compelling fashion. It is, indeed, the main focus of the book, relegating Charles Wallace (and Meg even moreso) to the status of watcher as events unfold.
The book is the deepest and most complex of the Time Quartet novels, but I didn't enjoy it as much as A Wrinkle in Time and A Wind in the Door. My reasons for this are quite fickle. Charles Wallace may be a fascinating character, and his exclusion from the O'Keefe family series of novels is unfortunate, but I wanted Meg to have a more active role in this story, pregnancy or no pregnancy. And relegating Calvin O'Keefe to a phoned-in cameo was unforgivable.
A Swiftly Tilting Planet still has to rank near the top of the eight Time Quartet / O'Keefe family series novels. It is the most ambitious and it is the best written. I fully expect to read it again and, perhaps then, I will be less fickle.