A great performance can often elevate a stock plot, and that's precisely what happens with "Ma." Octavia Spencer, who previously collaborated with director Tate Taylor on 2011's "The Help" (for which she won a Best Supporting Actress Oscar), is simply sensational in the title role. She plays Sue Ann Ellington, a lonely veterinarian's assistant who becomes dangerously wrapped up in the lives of a group of teenagers looking for a private place to drink and party. In her increasingly desperate attempts to fit in with kids more than half her age, Sue Ann—or Ma, as she prefers to be called—is reminded of a traumatic event she experienced when she was their age. Still haunted by these reverberating memories, she takes it as a personal affront when new-girl-in-town Maggie (Diana Silvers) and her friends begin to pull away.

"Ma" takes itself seriously, but not too seriously, with screenwriter Scotty Landes and the actors bringing a quirky sensibility to much of the dialogue and interactions. This tongue-in-cheek tone mixes well with a "...from Hell" narrative revolving around a series of parties that are all fun and games until they are violently not. The scenes focusing on the teens follow standard beats, a virtual drawbridge to introducing the fascinating, multi-shaded Sue Ann. Playing both a sympathetic victim and an unhinged antagonist, Octavia Spencer gobbles up this juicy part with relish, finding a way to pull at viewers' heartstrings one moment (even when the audience knows full well she is being manipulative) and severely creep audiences out the next. The radical extent of Sue Ann's psychopathy is suggested but not fully explored, leaving one to wish the picture were more focused on learning about her and less of a conventional horror-thriller. Still, Spencer gives her character depth even when the over-the-top, all-too-convenient third act starts to let her down.

As macabre entertainment, "Ma" fulfills its goal without really doing much more than expected (alas, this is one example where the theatrical trailer gives away far too much, softening what otherwise would have been some of the picture's best moments). Supporting turns from Juliette Lewis (2016's "Nerve"), as Maggie's caring, strong-willed single mother Erica; Luke Evans (2017's "Beauty and the Beast"), as Ben, a guy from Sue Ann's past; and a tiny but utterly disarming one from Dominic Burgess (2005's "Batman Begins"), as Erica's chatty new boss Stu, excel beyond their would-be thankless nature. Missi Pyle (2018's "Traffik"), as Ben's stuck-up girlfriend Mercedes, and Allison Janney (2017's "I, Tonya"), as Sue Ann's abrasive boss, veterinarian Dr. Brooks, are too talented for their barely-there roles, but they certainly class things up another notch. Just about every reason to see "Ma," however, begins and ends with Octavia Spencer. This is a long-time-coming star vehicle, one which casts a woman of color as a rare, front-and-center villain while nonetheless allowing her close to three dimensions. Take away the sizzling irons to torsos and the sewn-shut mouths and the film would arguably be even better for it: a forlorn character study of a woman who's been let down by life and marginalized one too many times.