There’s something wrong with senior citizens in The Elderly (Viejos). The record-breaking heat wave has them behaving eerily, and the temperature continues to rise. Filmmakers Raúl Cerezo and Fernando González Gómez, fresh off The Passenger, opt for slow simmering dread in an atmospheric examination of society’s alienation of the elderly. But the restraint and cryptic nature of the horror renders it more lukewarm than simmering.

At the start of the heat wave, Manuel (Zorion Eguileor, The Platform) lays in bed as his wife sits in another room, listening to music. Something switches within her, and she makes her way to the apartment’s balcony as if in a trance. The camera cuts here, making it ambiguous as to the cause of her fate, though the police chalk it up to suicide. In the wake of her death, Manuel’s son Mario (Gustavo Salmerón) wants his dad to move in with Mario’s family to look after him. Mario’s pregnant wife, Lena (Irene Anula), isn’t thrilled about the idea. At the same time, Mario’s teen daughter Naia (The Passenger’s Paula Gallego) toggles between concern for her grandfather and trying to settle into their new home. It quickly becomes apparent that Manuel isn’t well, and the rising temps exacerbate it. Worse is that Manuel isn’t the only elder acting weird.

Cerezo and González, working from a script that Cerezo co-wrote with Rubén Sánchez and Trigos Javier Trigales, play the horror close to the vest. The filmmakers offer up eerie motifs and hints that feel too inscrutable and struggle to wring suspense and dread out of many of them. The clues are there; the unsettling recurring song, eerie whispers, lurking neighbors, and enigmatic notes referring to “them” tease a larger terror driving the older residents to madness. Beyond hinting toward the larger picture, the clues remain unwieldy until far too late.

The horror is understated. Ignacio Aguilar’s stunning cinematography elevates the unsettling atmosphere; the sepia, orange, and burnt umber tones wash the shadowed apartment building in a haunting light. It makes the movement of the elderly residents downright creepy in parts. But just as a scene builds toward a potent scare, Cerezo and González pull back in favor of prolonged ambiguity. That ambiguity takes precedence over everything else until an intense finale that can’t compensate for the sluggish and overly mysterious build-up.

It doesn’t help that there’s a lack of cohesion among the characters. Mario, Naia, and Lena represent three different attitudes toward older people, from infantilism and guilt to repulsion. It’s clear that this slow burn is examining the treatment of senior citizens, but it’s unfocused. Mario’s unemployment factors into his relationship with Lena, but it goes unresolved and doesn’t seem to factor much into the overarching narrative. Naia lacks purpose other than as the film’s sole representative of youth.

The Elderly breaks up the narrative with cards that signal the rising temperatures, an on-the-nose means of signaling that the horror will crescendo to a fever pitch. While it technically does culminate in an unexpected and exciting finish, the slow burn getting there never manages to turn up the heat. It’s a technically well-made film emphasizing atmosphere and style, but the scares aren’t so effective, and its mysteries remain mostly inaccessible until the final moments.

The Eldery made its world premiere at the Fantasia International Film Festival.