In 1965, ten-year-old Willow begins to question her unusual life in the family's fortified compound deep in the woods. When she discovers a terrifying family secret, her parents convince her there is nothing to fear, but her father comes clean - once a month he turns into a horrific monster. When the monster escapes and they run for their lives, she must face the harsh reality of her father's identity and grapples with a life-altering decision.