This unprepossessing Spanish horror thriller, presented by Guillermo Del Toro, snuck into the Spectrum 8 Theatres a month ago with two showings per day and a “one week only” notice on the poster (and in the print ads). It’s still there, running daily in the late afternoon and late evening—and it will be there for another week, at least.

It’s always heartening when an unheralded film finds its audience, and The Orphanage is more than worthy of the attention.

The Orphanage begins with a flashback. A group of children are playing tag in front of the gloomy mansion that is the title institution; one, named Laura, is to be adopted and is called away from the others. Flash-forward three decades: Now the all-grown-up Laura (Belén Rueda) and her doctor-husband Carlos (Fernando Cayo) move into the renovated former orphanage with their too-cute young son Simón (Roger Princep). The idea is to turn it into a home for a small group of special-needs kids.

Unfortunately for the family, the mansion already has a full complement of special-needs children. Dead children.

The horror builds slowly as Laura and her son explore the beachside caves not far from the mansion. Mom is only slightly troubled when her son—a lonely kid with an overactive imagination—adds to his coterie of imaginary friends. Director Juan Antonio Bayona uses every trick in the haunted-house-flick book, filling the screen with shadows, teasing us with just-off-screen movement and tormenting the characters with strange noises and horrific screams. He’s not shy about gory violence in this part of the film, either, or introducing stock characters, like, for instance, a crazy old woman hiding in the orphanage’s former crematorium. There’s no irony or comedy in any of it, however—in fact there’s dramatic depth, as the strained personal dynamics in the less-than-perfect family build alongside the supernatural terrors. The cumulative effect is scary as hell. You will squirm in your seat.

Finally, everything comes to a tragic climax on the day Laura and Carlos are opening the house to the special-needs kids. The atmosphere is deliciously creepy, as the visiting kids put on masks and play—though one of the “visitors” isn’t from out of town. Bayona’s swirling camera and deft editing serve to both disorient and misdirect the audience’s attention.

Mystery layers upon mystery, and Laura begins to look for answers in the paranormal. (Geraldine Chaplin is affecting as a dead-serious medium.) Saying one word more about the story would be one too many. The less you know, the more you’ll enjoy the picture. Suffice it to say that the plot is brilliantly worked out to the last detail, betraying neither the supernatural nor the natural.

And, as with the last scene in producer Del Toro’s Pan’s Laby-rinth, you will be a stronger person than I if the ending of The Orphanage doesn’t choke you up.