Credit: Matt Kennedy/Lionsgate

What if the South won the Civil War? That may or may not be the premise of Antebellum — an intriguing exercise in speculative horror undone in the end by its own tangled messaging.

First-time filmmakers Gerard Bush and Christopher Renz open on a too-familiar scene: Casually cruel overseers, terrified slaves; a whip, and worse. While Confederate troops march through with their muskets and belles in hoop skirts float dreamily across the lawn, Eden (Janelle Monáe) slumps to the ground, dazed and traumatized. Even the smallest misstep — a moment of disobedience, a slow hand in the cotton fields, a wrong word to a white man, or even any word at all — could mean the end of her.

What the film’s first 40 minutes hold close, though, the trailer easily gives away: Eden is also Veronica, a post-bellum woman seemingly trapped in a mad antebellum world; one minute she’s a busy TED Talk type eating breakfast with her gorgeous family in a sun-drenched loft and taking Zoom calls, the next she’s back on the plantation begging for her life.

How those two impossible worlds come together, then, becomes the central mystery of the movie (due on VOD Sept. 18), and also its biggest stumbling block. Modern Veronica’s life — the adoring husband and adorable daughter, the fresh-cut flowers and hired town cars — looks lovely, but it’s all so Peloton-ad glossy and unspecific that nothing about it ever quite feels rooted in any real emotional universe.

Even the public speeches she partially makes her living by, mostly broad directives about courage and empowerment, sound oddly generic, particularly when the real Monáe has spoken so much more vividly to those same issues on her own time. There are brighter spots in the script: As her best friend, Gabourey Sidibe slides in almost from another movie, all girl's-night banter and cocktails, and Jena Malone (The Hunger Games) gets to sink her teeth into dual roles as a honey-dripping D.A.R., nearly giggling at her own villainy.

But most of the cast — including compelling actors like Jack Huston as a sneeringly genteel overseer and Kiersey Clemons as a desperate, furious slave — only get to skim the surface of their thinly sketched characters. (Though Bush and Renz, whose previous work is largely in high-end ad campaigns and music videos, seem to have a much firmer grip on their visual style; nearly every scene is lit and composed like a painting.)

Monáe, luminous, hardly needs to work to hold the camera: A gifted polymath who has managed to maintain a high-profile music career while making indelible turns in films like Moonlight and Hidden Figures, the star works valiantly to channel Eden/Veronica's pain and confusion, and the whole humanity of a life her captors so casually dismiss. As a performer, she commits utterly; if only the story could do the same. B–

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