In the middle of a New England winter, the boys accidentally disturb an experiment in their parents' lab. A sonic boom - a blast of heat - and the boys find they have been transported to a vast, trackless desert which is shaken by periodic earthquakes. Providentially, they encounter a water prospector named Japheth who offers to help them find refuge at the nearest oasis. Sandy and Dennys are intrigued by the creatures which accompany them on their trip through this (as they initially assume) alien world, which include a two-foot-tall mammoth and a pair of unicorns which appear simultaneously to be, and not to be; and humans shorter than average.
After a long ride through the desert during which they develop a severe case of heat stroke, the boys are separated when the unicorn Dennys is riding disappears. Sandy remains with Japheth and his elderly grandfather Lamech and is tended to by a variety of improbable beings, including a pelican. Dennys reappears in another tent, only to be bodily thrown into a refuse heap. Now seriously ill, he comes under the care of a friendly family with a large tent in the center of the oasis, headed by a gruff but kindly patriarch. As he recovers from his "sun-sickness", Dennys learns that his benefactor is in fact Japheth's father and Lamech's son - and his name is Noah. It soon becomes apparent that the boys have been transported back to Biblical times, just before the Great Flood. The pelican, scarab beetle and lion turn out to be the animal hosts of seraphim, who are surprisingly knowledgeable about quantum physics and twentieth century Earth. The nephilim, who also transform into animals, distrust the twins. They use their human wives to try to discover why Sandy and Dennys have come to the oasis, and whether they represent a threat.
Separated for much of the book, the twins become more independent of each other, and learn that neither they nor reality itself is as ordinary as they previously supposed. Both gain maturity over the course of about a year in the desert with Noah and his family. They each fall in love with Noah's daughter Yalith, but do not act on their desires. Dennys convinces Noah to reconcile with Lamech, and both twins eventually care for the old man's gardens as they wait to discover a way home. After Lamech's death, Sandy is kidnapped. He refuses to use violence to escape, and is eventually found by Japheth. Both twins worry that Yalith is not to be on the Ark, and neither are they. Nevertheless, they help to build the Ark before returning home via unicorn.
source: Wikipedia
