The Warning by James Patterson

Two roads lead to Mount Hope. None leads out. There's no place to run in a community that's been taken--and is being intentionally kept--off the grid. A small southern town was evacuated after a freak power-plant accident. As the first anniversary of the mishap approaches, some residents are allowed to return past the national guard roadblocks. Mount Hope natives Maggie and Jordan quickly discover that their hometown is not as it was before. Downed cellular networks fail to resume service. Animals savagely attack humans. And the damaged power plant, where Jordan's father is an engineer, is under military lockdown. As friends and family morph into terrifying strangers, the Maggie and Jordan increasingly turn to each other. Their determination to discover who--or what--has taken control of Mount Hope soon has them in the cross-hairs of a presence more sinister than any they could have imagined.