Archie Coomes lives in Seaham, a sleepy seaside town where nothing ever happens, but after his dad's construction company opens up the cliff beneath the old Langdon place, he feels like something evil is lurking around every corner of his hometown. When the adults in Seaham begin acting strangely, he and his friends Athena, Chris, and Oliver start to investigate. The friends soon find themselves diving into the town's history and uncover an ancient evil has awakened, and they are the only ones who can save their home.