By Madeleine L'Engle.
Of the books I've reread, I think this one was the best so far. The story is practically given away on the back cover (Sandy and Dennys walk into one of their father's experiments accidentally and find themselves in Noah's time), but emotionally it's very powerful. Some of the theology is definitely questionable and the ending was probably too simplistic, but the story has a lot of impact, while sticking pretty close to what the Bible says (when it says). L'Engle paints a picture of a people who are "wicked, thinking only of evil all the time", but who are in a sense very naive, possibly because they're so new to sinning.
It helps if you have a vague idea about what A Wrinkle in Time was about to understand a few brief references in here (to tessers and space travel), but it isn't really necessary.
Definitely recommended unless you abhor fiction completely and prefer to stick to practical shipbuilding...