It Follows Maika Monroe, Keir Gilchrist, Daniel Zovatto. Directed by David Robert Mitchell. Rated R. Opens Friday.

Though its title makes it sound like the first Twitter horror movie, David Robert Mitchell’s It Follows actually boasts a discomfitingly creepy, very physical premise. Teenager Jay (Maika Monroe) is chloroformed by her date immediately after they have sex, awakening strapped to a wheelchair. As it turns out, though, Jay’s assailant is now trying to warn her, not harm her. He just needs her to sit still while he explains (and shows her) what’s happened:

By sleeping with him, she’s contracted a curse. From now on, she’ll be relentlessly pursued by a malevolent force that’s always walking in a straight line toward her, no matter where on the planet she goes. While the thing can take any human form, it can’t move any faster than a brisk walk—it’s easy to outrun. But it never stops coming, ever. And the only way to get rid of it is to pass it to someone else, by having sex with them.

On its face, this sounds like yet another horror movie that serves as a metaphor for sexually transmitted diseases, in the tradition of early David Cronenberg. Mitchell arguably has something more nuanced and interesting in mind, tying into the evanescent nature of passion. It doesn’t really matter all that much what It Follows means, though, because the film tramples on your nervous system at every moment, forcing you to constantly scan the frame in search of innocuous background extras who might be moving slowly but steadily toward Jay. It’s like Where’s Waldo? if Waldo were a supernatural serial killer that can change shape at will.

Mitchell’s rules for this evil force don’t always make logical sense, and a climactic showdown at an indoor pool fizzles, but It Follows is still the best horror film to emerge in years. It lingers.