Linda has a seemingly perfect marriage with her rugged and handsome husband Mark and an adorable 8 year old daughter, Chloe. But when Chloe is injured by an elderly babysitter who has slipped into dementia, Linda wants to ensure that her child is never hurt again. Initially, Heather, the new babysitter, seems like the ideal addition to this practically perfect family. But Heather is a schemer who exploits the cracks in Mark and Linda's relationship, and delights in the resulting chaos. As Linda later learns, to her horror, Heather's intentions go far beyond the mischievous.
