Let me go back. In between A Wind in the Door and A Swiftly Tilting Planet, many years have passed. Meg and Calvin have married; Calvin is eminent in his studies, and Meg, having abandoned her excellent mathematical intelligence is pregnant with her first child.
The crisis of the book is brought forward at the opening when Mr. Murry receives a call from the President, asking for his help because a dictator, Mad Dog Branzillo, is threatening nuclear war. Mom O'Keefe, who came for Thanksgiving dinner, remembers a rune (essentially a prayer or phrase imbued with magic powers), which saves them from nasty weather (an over the top metaphor for impending doom). She gives this rune to Charles Wallace, and tells him he needs to stop Mad Dog.
He goes out to the star-watching rock to think about this, kything with Meg the whole time. There he meets a unicorn, whose mission it is to travel with him through time, which unicorns born from eggs can do by the way. They hop around randomly in time, and, at almost every time, Charles Wallace has to go 'within' a person there, which means that he can see things through there eyes and have a small impact on what they're doing. Basically, he just says the rune in all of the important places, so that he can make everything happy again.
Way to make a unicorn lame, Madeleine L'Engle. Also, what is with this rune business? Deus ex rune. Ugh. It is evident that L'Engle believes not in Christianity precisely, or, at least, not in Christianity as it is commonly worshiped. However, it is all bound up in her writing. This whole book is built around a family, who through generations have been reliving Cain and Abel. Lovely, I know.
Actually, that's not quite right. More like, two families who kept doing this, and the end result of their line was this Mad Dog Branzillo character. Of course, maybe that's because these two families kept intermarrying. I think the message I was supposed to get from this book was something about peace and goodness, but all I really got was that incest makes for badness, which I already fully believed.
When I was younger, I remember having loved the first book. I thought Meg and Calvin had this completely epic romance. They were one of the best couples in fiction, I think I thought at one point. Now, I have no idea why. There was only the slightest hint of romance in the first books. Then in book three they're married and pregnant. What the heck is that? Why would you skip the best freaking parts, L'Engle? And why can't Meg use her smarts that you spent the first two books proving she had?
Suffice it to say that I will not be reading Many Waters. It's been kind of fun revisiting these, but they're definitely not what I thought they were, which is another kind of entertaining. So sad when books are not nearly so good when read through the eyes of an adult.