Sandy and Dennys have always been the normal ones in their family, but one day, they accidentally intrude on one of their father's science experiments and find themselves living among angelic beings, dwarf mammoths, and unicorns. The twins will be drawn into a fierce struggle to control their families' destiny. Madeleine L'Engle once again creates a dazzling adventure in this fourth installment of the Wrinkle in Time Quintet.