The Threat Below by Jason Latshaw

SPSFC

She heard the legends. She knew the history. But nothing could have prepared her for what she found. Three hundred years ago, a lethal and mysterious threat arose and pushed humanity to the brink of extinction. Now, a small remnant - the descendants of the few survivors who escaped the massacre below - lives above the clouds, atop a mountain. When they discover their water supply is being poisoned, an expedition, including seventeen year-old Icelyn Brathius, must descend and face the horror that wiped out civilization centuries ago. The danger is closer than you think. The shocking true nature of the Threat Below. As Icelyn faces dangers in a world humans are not meant to survive, she learns that not everything is as it seems, uncovers an ancient revelation, and faces a choice that will change the fate of everyone above and below the clouds. Will Icelyn be strong enough to survive - and bear a terrible secret?