A lonely middle-aged woman befriends some teenagers and decides to let them party in the basement of her home. But there are some house rules: One of the kids has to stay sober, don’t curse, and never go upstairs. They must also refer to her as Ma. But as Ma’s hospitality starts to curdle into obsession, what began as a teenage dream turns into a terrorizing nightmare, and Ma’s place goes from the best place in town to the worst place on Earth.