Twenty-five years ago, the alien Givers came to Earth and bestowed upon the human race the greatest technology ever seen--four giant towers known as Ladders. Then, for reasons unknown, the Givers disappeared. Only a skilled crew of children can perform the maintenance necessary to keep the Laddertop stations up and running and back on Earth, competition is fierce to enter Laddertop Academy. Best friends Robbi and Azure, two 11 year old girls who are candidates for the academy, will become entangled in a dangerous mystery that may help them solve the riddle of the Givers--if it doesn't destroy Earth first.