A retelling of the Old Testament story of Noah's building an ark to hold his family and two of every animal during a flood God sent to destroy the world.
Not having been chosen by Noah, Achbar the mouse stows away on the ark and tries not to be discovered while he and the other animals await the end of the flood.
When the forty-first day on the ark dawns bright and clear, Mrs. Noah decides to do the wash, and having no rope long enough, devises an ingenious clothesline.
The fifteen-year-old Murry twins, Sandy and Dennys, are accidentally sent back to a strange Biblical time period, in which mythical beasts roam the desert and a man named Noah is building a boat in preparation for a great flood.