Title: Many Waters
Author: Madeleine L'Engle
What it's about: Twins Sandy and Dennys Murry are bamfed back to Biblical times when they mess with one of their father's space-time experiments. Finding themselves in a well-known story from the book of Genesis, they lend their aid to the family who saved their lives and end up learning about themselves and about love.
What I thought: Simple but rich descriptions and a novel premise make this a book I've always been fond of. Religious lore is heavily drawn on, but there's no preachy moralizing, so it's all good. The characters are well-drawn, and the depictions of antediluvian life are interesting.
Overall: Probably makes the most sense if you read it in sequence with the rest of L'Engle's Time Quartet books.