A Swiftly Tilting Planet (paperback)

In A Swiftly Tilting Planet by Madeleine L'Engle, a companion to the Newbery Award winner A Wrinkle in Time and A Wind in the Door, fifteen-year-old Charles Wallace and the unicorn Gaudior undertake a perilous journey through time in a desperate attempt to stop the destruction of the world by the mad dictator Madog Branzillo. They are not alone in their quest. Charles Wallace's sister, Meg--grown and expecting her first child, but still able to enter her brother's thoughts and emotions by "kything"--goes with him in spirit.