Many Waters by Madeleine L'Engle is about twin brothers who accidentally tamper with their father's experiment and get sent back in time to biblical prehistory where people live for hundreds of years and mythological creatures are commonplace. They are unprepared for the extreme desert climate and suffer from extreme sunburn and heat stroke. Some natives, who turn out to be the family of the biblical Noah, help nurse them back to health. After the twins realize where and when they are, they must race against time to figure out a way to get home before the flood waters come.
I really enjoyed this book and especially liked how the author drew from non-traditional religious sources such as The Book of Enoch. I also really liked some of the spiritual themes in this book which seemed universal even if it is based on a Judeo-Christian story. I would recommend this book to anyone who enjoys biblical fantasy or enjoyed the author's other books. Although this book was written after A Swiftly Tilting Planet, it actually takes place before that book. I personally prefer to read these books in chronological order, but I would only recommend that others do so if they don't mind taking a break from the main characters that feature in the first three books of this series.