On the afternoon following Mrs. Whatsit's visit, Meg and Charles Wallace walk over to Mrs. Whatsit's cabin. On the way, they meet Calvin O'Keefe, a popular boy in Meg's school whom Charles considers a kindred spirit. The three children learn from Mrs. Whatsit and her friends Mrs. Who and Mrs. Which that the universe is threatened by a great evil called the Dark Thing and taking the form of a giant cloud, engulfing the stars around it. Several planets have already succumbed to this evil force, including Camazotz, the planet on which Mr. Murry is imprisoned.