Helena, a woman living a seemingly ordinary life, hides a dark secret: her father is the infamous “Marsh King,” the man who kept her and her mother captive in the wilderness for years. After a lifetime of trying to escape her past, Helena is forced to face her demons when her father unexpectedly escapes from prison.

The successful children's writer Claire Holloway is troubled by scary nightmares and is under psychological treatment. While working out watching television, she sees the landscape of the Rose Marsh Farm in the Westmoreland County, and she notes that the farmhouse is linked to her nightmares. She decides to spend her vacation in the farm, which is located nearby a swamp, and she is haunted by the ghosts of a little girl and a teenage boy inside the house. She is befriended by the local publisher and historian Noah Pitney but after a sequence of disturbing visions, she decides to contact the paranormal consultant Geoffry Hunt. Together, they investigate the mystery and disclose a tragedy that happened in the farm about twenty years ago.