The movie follows the life of Grace Stweart ( Nicole Kidman) and her two young children who are living in a remote country house just after a war (I can't remember if it i was WW1 or WW2) and now they have an isolated life that is simple and nice. Although it isn't clearly explained, Grace appears to be someone of reasonable wealth as she employs servants and the house is enormous.

The children are photosensitive and can actually suffer great harm if exposed to sunlight, this condition is called Xeroderma Pigmentosum (although I may have spelled that wrong) and is a very rare, yet very real physical condition.

The children must therefore be kept out of sunlight at all times.

The movie becomes spooky pretty quickly as it becomes evident that the house is haunted with a child named Victor and his family (I think) who claim that the house is "theirs." While it is subtle at first, the presence of the spirits becomes more and more prevalent and while there isn't a great deal of "jump scares" there are plenty of "dread scares" (I am not sure if either of those are real terms - i hope you know what i mean.)