If your favorite scene in The Help was the part where Octavia Spencer made a racist eat her poo, you’re going to love Ma. Heaven knows I do. Octavia Spencer is in unbridled revenge mode, giving a masterfully broad performance in a smart, scary cautionary tale.

Ma stars Diana Silvers (Booksmart) as Maggie, a teenager moving back to her mother’s small rural hometown. Her mom, Erica (Juliette Lewis), is a single parent and struggling financially, so Maggie gets left home alone a lot while Erica picks up extra shifts at the casino where she serves drinks. When the opportunity comes to hang out with kids her own age, Maggie goes for it, and now it’s her job to find an ethically-malleable adult to buy them alcohol for adolescent party reasons.

That’s when they bump into Sue Ann (Spencer), a veterinarian who – after some cajoling, and after recognizing whose father owns the van they’re driving- buys them booze. She also offers to let them drink in her basement, so at least she’ll know they’re safe. What’s that? Oh, upstairs? You can’t go up there. That’s the only rule of the house. Nothing suspicious about that at all. Who wants shots? Invite your friends! Invite ALL your friends!

Ma looks a heck of a lot like a film about the dangers of teen drinking, but it doesn’t stop there. Directed by Tate Taylor (The Help) and written by Scotty Landes (Who Is America?), the film is a relatively scary story about teenagers whose relatively minor rebellions backfire, putting them in the crosshairs of a psychopath who forms an unhealthy attachment to partying with teenagers, and who demands their attention at all hours… or else.

But as acceptable as that straightforward horror story about teenagers would be, Ma is Octavia Spencer’s film. It was very nice of her to let some of the other actors drive it for a while, but now she’s here and she’s going to dominate every scene. She dances, she threatens, she endears and she pesters. There’s something deeply wrong with “Ma,” as she comes to be called, and the movie knows that her story and her vengeance is all that really matters.

The origin of Ma is a horror story in-and-of itself, and without giving anything away, it goes far beyond the teen drinking public service announcement the movie plays like in the first half. Taylor’s film shines a light on the legacy of trauma and follows it to frightening conclusions, revealing how and why Ma is trapped in a state of suspended adolescence, and what her life has become in the years that followed. Her life is pain, and now that pain will be inflicted on others.

Ma doesn’t take place in a vacuum. It takes place in a small town where intergenerational dramas play out on a daily basis. High school jocks never lose their hero status, even when their marriages fall apart. The sons of those jocks internalize ugly behaviors, and say atrocious things about other women to their girlfriend’s mothers. The people who pulled unspeakable pranks in high school think nothing of it decades later because they feel like their legacy is secure, that they’re still somehow on top – even when they’re broke – and so they have no need for self-reflection.

But all Sue Ann has is self-reflection, a lifetime of missed opportunities and socializations, and an anger of the highest caliber that has been repressed for decades. As “Ma” she has the opportunity to become the center of attention, and when the teenagers get creeped out – as anyone would – their rejection goes badly, badly, badly.

Tate Taylor’s thriller isn’t in a rush to get to the violence. If anything it could impersonate a straightforward drama for at least half of the running time. But we know it’s a horror movie and so do the filmmakers, and they make the wait well worth it. Ma’s violent streak has some eery outlets, and at least one person dies in a way that even diehard horror fans will have to admit is extremely disturbing and distinctive.

And throughout all that bravura third act violence, Spencer’s performance just keeps getting better and better. She’s peeling the layers off a rotten onion, and each step reveals another fascinating – but disturbing – facet of her character. Her pain is never forgotten, even at her most sadistic. Her wickedness is always underneath the surface, even when she herself has no idea it’s in there. And she’s always viciously funny, as though she really does know it’s her movie, so she gets to do and get away with anything she wants. At least for a little while.

The movie itself is a little longer than it needs to be, even though it compensates in the finale, but Octavia Spencer’s “Ma” has the potential to become a classic horror villain. However this movie ends (and I’m not saying a word), halfway through the running time it’s already clear that she could headline her own franchise. And if Octavia Spencer is up for it, let’s hope she does!