In A Swiftly Tilting Planet L'Engle explores what appear to be cyclic events in human history. The story of Madoc and Gwydyr, for example, parallels the biblical story of Cain and Abel. Trouble arises between the two brothers when one grows jealous of the other, and they part company over Madoc's love, Zyll. These three character "types" repeat themselves through all of the history that Charles Wallace, Gaudior, and Meg investigate. They are next encountered in Salem, Massachusetts, as the townspeople attempt to execute the half-Indian woman, Zylle, for witchcraft. In this "incarnation" the original triangle is joined by a sanctimonious minister, Duthbert Mortmain, who, although he says that he represents God's will on Earth, actually perverts the gospel of love to meet his own selfish ends. Zylle is saved by a powerful magical incantation given to Ritchie Llawcae by the American Indian, Zilla...