Patty McCormack's "Mommy" is psychotically obsessed with her 12-year-old daughter Jessica Ann -- so much so that when she finds out Jessica didn't get the "Student of the Year" award again, she solves the problem by murdering the teacher who didn't recommend her for it. She dismisses the killing as inconsequential ("a minor accident"), but the homicide detective assigned to the case suspects her immediately, and an insurance investigator who also suspects her tries to get close to Jessica Ann to find out what really happened.
