The Spanish thriller “Viejos,” aka “The Elderly,” is a creepy, doom-laden sci-fi parable that doesn’t quite close the deal, a film of slow-building suspense whose climax lacks the clarity of intent and the level of terror in the performances to pay off.

But filmmakers Raúl Cerezo and Fernando González Gómez give us something to chew on, even if they haven’t wholly digested their ideas themselves.

Heat waves are always tragedies for the elderly, especially in the under-air-conditioned corners of a climate-changed planet.

Such a Spanish heat wave is the backdrop to this story of old people seemingly going crazy and dying, with the young, “who never listen” to them, missing the signs that something grimmer and less explicable is in play.

The thermometer is just under 110 (42 degrees Celsius) when Rosa (Ángela López Gamonal) hears the forecast, takes the measure of her past, her present and the future and leaps to her death in front of silent witness neighbors and her husband, Manuel (Zorion Eguileor), staring in sweat-stained but understanding shock at her action.

She got tired of “hearing” (in Spanish with English subtitles) one surmises. What? Her grief-stricken son Mario (Gustavo Salmerón) doesn’t get it.

“It’s the static noise, the magnetic waves,” his father tries to explain.

The audience’s surrogate in this story might be Mario’s rebel teen daughter Naia (Paula Gallego). She gripes to her boyfriend Jota (Juan Acedo) how “gross” old people’s lives are. “Nobody listens to you” when you’re old.

Jota may have a clue, too. “Old people know what’s coming,” he reassures her. They aren’t scared, or at least Jota insists he won’t be.

But there’s something not right about the seniors of the city right now, and Manuel could be a case study in what it might be. He’s not grieving, not really in shock and yet not “right.” Not at all.

He obsesses over transistor radio parts, resists moving in with Mario and his disapproving second wife Lena (Irene Anula). And as much as he “relates” to his granddaughter, his query about Naia’s dead mother is telling, or would be if the curious teen was on the same wavelength.

“Does she talk to you at night?” grandpa wants to know. Because he’s sure “Rosa,” his late wife, is still around and “coming back.”

The sanest character in the lot might be pragmatic Lena — pregnant, dealing with a teen who likes reminding her she’s “not my mother” and a husband who insists on taking his scary dad in at this moment of crisis.

All will be tested as the temperature steadily rises into the 120s, grandpa’s behavior grows more dangerous and nobody seems to grasp the gravity save for Lena.

I put a lot of stock in actors getting across the meaning of a scene, the level of threat or simple misery (heat-caused, in this case) their characters must feel. And that hits you as “off” early on in “The Elderly.”

The seniors are suffering, but Mario — an unemployed AC installer who has no work because “the country’s broke” — just escapes to the bar downstairs, Lena sweats and frets and Naia just changes outfits and takes grandpa’s side in all things, especially when the phrase “nursing home” is trotted out.

That blunts the narrative’s effectiveness, and seriously undercuts the climax. Character reactions are either amusingly unrealistic or simply passive and frustrating.

The climate change heat allegory would have been enough to drive the plot, but the script reaches for something more cryptic that the “You never listen to me” elders are responding to. That doesn’t need to be explained, but the way the third act unfolds, a little something to grab hold of that’s “realistic” would’ve helped.

The violence is jolting enough, if zombie-movie slow in most cases.

And while the gloom never lifts and the suspense finds a foothold just often enough to maintain interest, the climax is a serious stumble and makes one wish the ending had been worth all that slowly unraveled before it.

Rating: unrated, graphic violence, sex, nudity, profanity, smoking

Cast: Zorion Eguileor, Paula Gallego, Gustavo Salmerón, Juan Acedo, Ángela López Gamonal and Irene Anula

Credits: Directed by Raúl Cerezo and Fernando González Gómez, scripted by Javier Trigales, Raúl Cerezo and Rubén Sánchez Trigos. A Dark Star release.

Running time: 1:33