Linda appears to have an idyllic life with her charming husband, Mark, and their delightful 8-year-old daughter, Chloe. However, when Chloe is harmed by an aging babysitter suffering from dementia, Linda becomes determined to protect her daughter from future harm. At first, the new babysitter, Heather, seems to be the perfect fit for their nearly flawless family. Yet, Heather is actually manipulative, taking advantage of the underlying issues in Mark and Linda’s marriage and reveling in the turmoil she creates. To Linda’s dismay, she eventually discovers that Heather’s plans are far more sinister than mere mischief.