Deb and Tony have just begun their life together. With their first child on the way, the hardworking couple moves into a picturesque home in Atchison, Kansas, hopeful about the future.

But when their son is born, the child's toys seem to take on a life of their own. Deb is intrigued, but she thinks that her son has a ghostly playmate. Curiosity turns to horror when Tony is tormented by strange whispers, ghostly footsteps and bloody wounds that seem to have been caused by the spirit of a deceased 7-year-old girl.

A psychic warns that she is not the cause of the violence. There is something much darker inside the home, controlling the dead child‚ and desperate to take control of the living.

The Bible recounts a tale in which Jesus and his disciples came upon a pariah who was possessed. When Jesus asked the man his name, he replied that there was a legion of devils inside of him.

In Brookfield, Connecticut, 12-year-old David suffers from intense nightmares of an old man with demonic features. In his mind, the boy sees the old man flying toward his home, and his fear of impending doom grows day by day. David's mother is unsure of how to respond‚ until they see their son get physically attacked by an invisible entity.

The family contacts paranormal investigators Ed and Lorraine Warren, who make contact with a legion of demons inside the child's body. The Warrens know that, if they do not face the evil, David's soul will be consumed by darkness.