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Madeleine L'Engle
American writer
Many Waters
Sandy and Dennys Murry, usually the most ordinary of their extraordinary family, find their lives upended when a scientific experiment sends them hurtling through time and space. Stranded in a prehistoric desert, they encounter mythical creatures and a world on the brink of a great flood. To find their way home, they must navigate ancient conflicts and help a man named Noah prepare for an ark.
This novel functions as a standalone story because it shifts the focus to the twin brothers who are only minor characters in the earlier books. While it is part of a larger series, you can follow the plot and character arcs without having read the preceding titles.
Although it was published as the fourth book in the series, the events in this story take place chronologically between the second and third books of the quintet.