Many WatersMany Waters

A touch of computer keys, a blast of heat, and suddenly the Murry twins, Sandy and Dennys, are gasping in a shimmering desert land.  If only the brothers had normal parents, not a scientist mother and a father who experiments with space and time travel.  If only the Murry twins had noticed the note on the door of their mother's lab: Experiment In
Progress.  Please Keep Out
But it's too late for regrets.  There's a strange-and very small-person approaching, with a miniature mammoth in tow. . . .
At last it's Sandy and Dennys's turn for an adventure-an adventure that turns serious when they discover that "many waters" are coming to flood the desert.  The twins must find a way back home soon, or they will drown.  But how will they get back to their own time?  Can they?