No one can explain the strength of a mother's love. A woman who carries a child inside her for 9 months and nurtures them as infants..... Only to one day become their killer. Diane Downs, Andrea Yates, Marybeth Tinning and Susan Smith are mothers who crossed that line of love and killed their own children. We will explore their lives and their crimes and journey through the courtrooms, as we try to find out what made these mothers turn into MOMSTERS.