Sparrow Rock — Nate Kenyon

They were just a group of high school kids looking for a place to party. They didn't know the end of the world was coming. Now, alone and trapped belowground in a state-of-the-art bomb shelter, they are being stalked -- and the creatures that come for them through the dirt and ash are like nothing anyone has ever seen before.
There is a new ruling life-form on earth, and these six humans are the only remaining prey.