When Isla March learns her grandmother has vanished, she returns to Greyhook, Washington, the fog-shrouded coastal town she once tried to leave behind. In the March House perched high on the bluff, she uncovers cryptic journals, unsettling letters, and whispers of something ancient tied to her bloodline. As tourists are drawn into the water and locals begin to disappear, Isla begins to fear the ocean's pull is no coincidence, and uncovering the truth will mean confronting whatever has long been buried beneath the tide.