Jessie and Mark Hobson (Kate Bosworth and Thomas Jane) haven't been the same since the loss of their young son, Sean. Trying to heal, they take in a foster child--8-year old Cody (Jacob Tremblay), who does everything he can to avoid falling asleep.

Cody's dreams become real when he sleeps. One night, Jessie and Mark are shocked when an image of their dead son appears to them. Longing to see Sean again, the Hobson's visit with their "son" at night while Cody sleeps.

Cody becomes tormented by a gaunt, monstrous vision of horror known as "The Canker Man". As Jessie and Mark try to get Cody to sleep, his nightmare creeps more into their lives, putting the Hobson's in grave danger.