Let’s talk about endings: Don’t you hate them, particularly when one doesn’t hit the mark? All’s well that ends well, of course, and lord knows there are as many endings as there are stories to tell, but a destination should be worth the trip, don’t you think? 

A 19th-century American poet, Henry Wadsworth Longfellow, noted that “great is the art of beginning, but greater is the art of ending.” Longfellow was speaking of mortality, but the analogy holds because it presupposes a simultaneous sense of unity and completion.

All of which is a roundabout way of noting that the ending of Jason Yu’s tidy horror film, “Sleep,” is too tidy for its own good. Up until the last 10 minutes or so, the picture is cunningly duplicitous in the curves of its plotline. The story has few characters, but it has many facets and Mr. Yu juggles them adroitly. That he settled on one and only one upshot leaves the audience flat-footed: Couldn’t he have found a way to sustain the suspension of gravity?

Here I should mention that “Sleep” is a pretty good movie. For the most part, it’s tight-knuckled, deliberately calibrated, and involving. Mr. Yu, who directed his own screenplay, comes with accolades in tow, not least from the Oscar-winning director of “Parasite” (2020), Bong Joon-Ho. Mr. Bong avers that “Sleep” is “the smartest debut film I’ve seen in 10 years.” Should we take this commendation with a grain of salt, given that Mr. Yu once served as assistant director to Mr. Bong? Maybe, but a boss’s recommendation shouldn’t be dismissed lightly.

The two primary cast members, Lee Sun-Kyun and Jung Yu-Mi, are inordinately appealing. American audiences will recognize Mr. Lee from “Parasite” and Ms. Jung from a rip-snorting zombies-in-transit opus, “Train to Busan” (2016).  Here, they play Hyun-su and Soo-jin, a recently married couple expecting their first child. They live in a neatly appointed home within a notably generic apartment block, a discrepancy that mirrors the inside/outside dynamics of the plot’s central rub.

“Someone’s inside” is a phrase Hyun-su mutters in his sleep one evening, and Soo-jin has a hunch that it doesn’t augur well. Hyun-Su, a struggling actor, sloughs off his wife’s concerns: The words are part of the script on which he’s currently engaged. Still, hubby begins to act oddly during the nighttime hours. Their apartment is suddenly prone to all sorts of bumps-in-the-night — windows knocking, doors creaking, like that. Mr. Yu sets up these haunted house conventions in a manner that is deadpan and stylish. They’re a lot of fun.

Then, things get serious. Hyun-su begins scratching his face during his slumbers — so much so that he loses his current acting job, as no amount of make-up can cover those wounds. On other nights he’s making raids on the fridge in a catatonic state; the preferred snack is meat, the rarer the better. Upon waking, Hyun-su has no memory of engaging in these activities, and Soo-jin is soon doing internet searches on sleep disorders. A doctor is visited; drugs are prescribed. The couple’s Pomeranian, Pepper, knows that the status quo has gone awry.

In the meantime, there’s Min-Jeong (Kim Gook-hee) to deal with. She’s the downstairs tenant who has only just inherited her father’s apartment. Talk about passive-aggressive: Min-Jeong is prone to caustic commentary even as she feigns neighborliness. When Hyun-su’s sleep problems continue, Soo-jin’s mother (Lee Kyung-Jin) gives in to her meddlesome ways and hires a shaman (a sternly attractive Kim Keum-Soon) to do her particular whammy in the household. Hyun-su considers all of this with a jaundiced eye. His wife? She’s starting to believe in all this hocus-pocus.

At which point, “Sleep” teeters between abiding rationalism and otherworldly portent, all the while calling into question the perceptions of everyone involved. Mr. Yu navigates a line between over-the-top anxiety and trepidacious comedy, and manages to maintain an ambiguity as to what, exactly, is going on and who (or what) is responsible for it. Would that our erstwhile director built upon that ingenuity rather than squander or, at least, lessen its promise. But here is a movie of impressive promise, compositional acuity, and not a few chills.