When single mother Liv is commissioned to paint a mural in a 100-year-old lighthouse on a remote Scottish island, it's an opportunity to start over with her three daughters—Luna, Sapphire, and Clover. When two of her daughters go missing, she's frantic. She learns that the cave beneath the lighthouse was once a prison for women accused of witchcraft. The locals warn her about wildlings, supernatural beings who mimic human children, created by witches for revenge. Liv is told wildlings are dangerous and must be killed. Twenty-two years later, Luna has been searching for her missing sisters and mother. When she receives a call about her youngest sister, Clover, she's initially ecstatic. Clover is the sister she remembers—except she's still seven years old, the age she was when she vanished. Luna is worried Clover is a wildling. Luna has few memories of her time on the island, but she'll have to return to find the truth of what happened to her family. But she doesn't realize just how much the truth will change her.