 Sandy Murry is quoted as having said that "some things have to be believed to be seen", a lesson he learned in "Many Waters".There is also a reference to Kate Murry's lab being twice tampered with in the beginning of the book, clearly referencing the actions of Sandy and Dennys of "Many Waters", although the Murrys attribute the break-in to some "local kids".Last but not least, Polly's experience with the People of the Wind is consistent with Charles Wallace's interactions with the same tribe in "A Swiftly Tilting Planet".