Harlan is the sheriff in a remote Appalachian town. He fell in love with his best friend Andy’s wife. Andy is now bent on revenge and Linda is caught in the middle. Andy works as a coal miner. During his shift, the men cut into an ancient underground chamber and release an evil entity that has been imprisoned there for millennia. When the entity escapes it ignites a gas explosion that kills all the miners – including Andy. Linda and Andy have a son named Tom. He is in a relationship with Harlan’s daughter Jessie. When Tom learns of his father’s death, he takes his anger out on Harlan and Linda. Then Tom and Jessie run away to the hunting cabin their fathers once shared. Brutal deaths start happening in the area and Harlan investigates. Soon it becomes apparent that there is something supernatural going on and Harlan retrieves the two reluctant teens from the cabin. When they return to town it looks like a disaster area. Everything is on fire and the streets are filled with terrifying, bloodthirsty creatures. The trio arm themselves and fight their way through the carnage to find Linda and escape. During this ordeal they see an apparition that looks like a grotesque version of Andy. When they finally get to Linda’s house, she is gone and there is a message from Andy saying he has her at the mine. Harlan goes to rescue her and the kids refuse to be left behind. However, they become separated in the mine during their search and Harlan confronts Andy alone. The entity the miners released now inhabits Andy’s mangled body and both of their personalities compete for control of it. Andy wants to use his newfound power to make Harlan pay for his betrayal. Harlan asks about Linda and she comes forward. She has been turned into one of the creatures that they saw in town. Harlan is crestfallen and then Andy attacks him. Just then the teens arrive and start unloading their guns into Andy. He falls back into the pit from which the entity escaped. Linda and all the other creatures immediately collapse. Andy was the link between them and the entity and that link is now broken. Then the monstrous, ethereal being comes rocketing up out of the pit again. Harlan and his charges flee. The kids race ahead and Harlan gets injured. He can’t catch up and has to confront the otherworldly creature. Harlan realizes he cannot outrun the thing and that it is going to possess him just as it did Andy. It will then resume spreading its horrifying reach into the world. Harlan is wearing a methane detector that indicates there is gas in the mine. He knows he is doomed so he ignites the methane to trap the entity here and save everyone else. His plan works and the teens manage to get out of the tunnel just before it collapses – sealing away the mine and the evil entity forever.