LindahasaseeminglyperfectmarriagewithherruggedandhandsomehusbandMarkandanadorable8yearolddaughter,Chloe.ButwhenChloeisinjuredbyanelderlybabysitterwhohasslippedintodementia,Lindawantstoensurethatherchildisneverhurtagain.Initially,Heather,thenewbabysitter,seemsliketheidealadditiontothispracticallyperfectfamily.ButHeatherisaschemerwhoexploitsthecracksinMarkandLinda'srelationship,anddelightsintheresultingchaos.AsLindalaterlearns,toherhorror,Heather'sintentionsgofarbeyondthemischievous.