The Destroyers

The year is 2134. Libby is one of the only humans left. Everybody else is a Destroyer or dead. Destroyers are fast, 3-eyed monsters with beefy bodies. They kill everybody except for a select few but only the Destroyers know why those ones aren't killed. It's a been 5 years since Libby's family died. One year since Adrian, Libby's boyfriend and her best friend's twin brother, ran away to find the Destroyers. Two days ago, Libby's best friend, Ally was attacked by a Destroyer but he stopped when he saw her neck and ran away with her, Now she is in training to become a Destroyer and Adrian appears outside Libby's hiding spot, a treehouse, but there's a catch....What will happen next?