Grace is a religious woman who lives in an old house kept dark because her two children, Anne and Nicholas, have a rare sensitivity to light. When the family begins to suspect the house is haunted, Grace fights to protect her children at any cost in the face of strange events and disturbing visions.

A woman named Grace retires with her two children to a mansion on Jersey, towards the end of the Second World War, where she's waiting for her husband to come back from battle. The children have a disease which means they cannot be touched by direct sunlight without being hurt in some way. They will live alone there with oppressive, strange and almost religious rules, until she needs to hire a group of servants for them. Their arrival will accidentally begin to break the rules with unexpected consequences.