When Edna (Robyn Nevin) mysteriously vanishes, her daughter Kay (Emily Mortimer) and granddaughter Sam (Bella Heathcote) travel to their remote family home to look for her. As Kay discovers mounting evidence that her mother is suffering from dementia, creeping dread turns to panic. Suddenly, as inexplicably as she disappeared, Edna returns, with no memory of the past several days. Soon after her return, Kay and Sam begin to discover a sinister presence haunting the house and taking control of Edna. Is this simply the horror of dementia or is something more sinister at play?