By marrying that universal fear to a heartbreaking story about family and mental illness, David F. Sandberg created more than a viral gimmick. He created a modern nightmare. So go ahead. Turn off the lights. But maybe keep your phone charged.

The plot kicks into gear when Rebecca’s younger half-brother, Martin (Gabriel Bateman), begins seeing Diana in their mother’s house. Child Protective Services gets involved, and Rebecca must rescue her brother while grappling with the fact that the monster isn’t just a ghost—it is the physical embodiment of her mother’s suicidal depression.