A simple, downbeat and taut-as-a-drum vengeance thriller, “Eye for an Eye”(Quien a hierro mata) lives up to the promise of its simple, evocative title.

It’s about a crime family in Cambadoas, in Spanish Galicia, the northwest coast of the country facing the harsh Atlantic. And it’s about drugs, double-crosses and a thirst for revenge that lingers for years and years.

The Padín brothers are heirs to an empire that includes seafood fishing, processing and restaurants — and drugs. But they’re anxious to expand. It’s just that ruthless Toño (Ismael Martínez) and hotheaded Kike (Enric Auquer) can’t get their old man to sign off on it.

Old Antonio (Xan Cejudo) is in prison, about to get out. He wants nothing to do with a deal that includes the murderous Colombians and Chinese dealers he knows nothing about. And he wants nothing to do with his family, either. When he’s out the enfeebled old man wants to live in the state nursing home.

That’s where Mario (Luis Tosar) is head nurse. He’s good with patients, happy that he and his wife Julia (María Vázquez) are expecting their first child.

He gives nothing away when his infamous new patient shows up. He not only knows who Antonio is — he jokingly calls him “mayor” — he has an idea of why he’s there. He wants to die in peace.

“Better a little indifference” to the indignities of old age, Mario speculates (in Spanish with English subtitles), “than pity?”

And he meekly takes the gruff threats of Kike when the two sons show up to try and get the old man to sign off on their plans. But in between Lamaze classes, patient care and staff meetings, Mario is thinking something through. What is he up to?

Horror director Paco Plaza (“Veronica”) steadily builds the suspense tucked into the Juan Galiñanes and Jorge Guerricaechevarría script, and he and his production team add generous helpings of dread. This is an overcast place, a town small enough where people know each other, especially those with any dealings with the underworld.

Mario knows this world. And when a junkie cryptically remembers, “You were dead,” we start to understand.

I love the way the script grapples with its subtext, losing control of one’s life, senses and bowels in extreme old age. “We think we can control everything, and in the end, just nothing.”

And the film’s somber, almost funereal tone beautifully builds the dread that a ticking clock third act — when plans are set, and undone.

Tosar’s beard helps him maintain a poker-face in most of his dealings with the increasingly frantic mobsters, Martínez and Auquer amp up their agitation as their scheme unravels and Vázquez evolves from a giddy and playful mother-to-be to a wife who knows her husband too well to not know something is up.

If nobody in Hollywood has snapped up the rights to this for an English-language remake, they’re missing the boat. “Eye for an Eye” is a simple sharp Spanish thriller that rarely blinks.

MPAA Rating: TV:MA, violence, profanity, drugs

Cast: Luis Tosar, Xan Cejudo, Ismael Martínez, Enric Auquer, María Vázquez

Credits: Directed by Paco Plaza, script by Juan Galiñanes and Jorge Guerricaechevarría.  A Netflix release.

Running time: 1:47