The Cairn's (Sam Rockwell and Vera Farmiga) have it all: good marriage, nice apartment, a gifted nine-year-old son, Joshua, and a baby on the way. When their second child arrives, the young boy begins to resent his parents constant doting on his new sister. Suddenly, a series of tragic events fill the Cairn household with utter despair and unspeakable horror. The events leave the family questioning if it's all a series of eerie coincidences... or the calculated agenda of a sinister sibling with the perfect plan for revenge?