In the middle of a
New England winter, identical twin brothers Sandy and Dennys accidentally disturb an experiment in their parents' laboratory and are teleported to a sandy desert. There, they are acquired by water-prospector 'Japheth' and guided to an
oasis, but Dennys is separated from the others. Sandy remains with Japheth and his elderly grandfather
Lamech; there, Sandy is cured of heatstroke by a variety of improbable beings, including
seraphim. Dennys reappears in another tent and is thrown into a refuse heap. He later comes under the care of a friendly family in the center of the oasis, headed by a gruff but kindly patriarch called
Noah. It soon becomes apparent that the boys have been interpolated into the story of
Noah's Ark, shortly before the Flood. Both Noah and Lamech receive mysterious instructions from God (known as El) concerning the building of the Ark. The twins come to understand that unicorns who can traverse space and time live in the oasis. Sinister supernatural beings known as the
nephilim distrust the twins, and their human wives attempt to gather information about them. At several points, the wife of a nephil unsuccessfully attempts to seduce Sandy. Separated for much of the book, the twins become more independent of each other and gain maturity over the course of a year in the desert. Both are in love with Noah's beautiful and virtuous daughter Yalith (and she with them), but neither twin declares his affection until the very end of the novel. Dennys convinces Noah to reconcile with his father, Lamech, and both twins eventually care for Lamech's gardens while he lies ill. After Lamech's death, Sandy is kidnapped, but is eventually found by Japheth. Suspense arises when it becomes clear that there is no place on the Ark reserved for Sandy, Dennys, or Yalith. After both twins assist in the construction of the Ark, Yalith is taken by the seraphim to the presence of El. Sandy and Dennys are then returned to their own time and place by
unicorns summoned by the seraphim. ==Major themes==