Cinema has always been fascinated by androids. From “Metropolis” to “Blade Runner,” the juxtaposition of humans next to their artificial form has provided endless hours of stories that can be as exhilarating as they are poignant. Tough moral questions about consciousness and humanity go down easier when hidden under the glossy sheen of genre, after all.

With so many now-classics preceding it, “Ex Machina” might seem like just the latest flavor in the android movie shop. And yet, without necessarily expanding on this well-trod territory or innovating contemporary science-fiction, by going deep on a simple construct, “Ex Machina” establishes itself as a unique and deeply unsettling psychological thriller that’s both necessary and unforgettable.

The construct in question: How good is this android?

Writer-director Alex Garland in his feature debut tells the story with basically only three characters: Caleb (Domhnall Gleeson), the sharp programmer whose life is upended to spend a few days in a remote location with his company’s billionaire CEO and brilliant recluse, Nathan (Oscar Isaac); and Nathan’s creation, Ava (Alicia Vikander).

Caleb thinks he’s won a prize and a retreat with a genius. It’s only when he arrives that Nathan tells him his real purpose is to advise Nathan on whether or not Ava passes the human or machine test.

Nathan’s home embodies the modern design ideal of organic architecture and he and Caleb discuss Ava as Schubert and Bach play faintly in the background. Big, fascinating ideas fly around at rapid speed, but “should” does not seem to be in their vocabulary.

Garland builds a subtle tension by making everything slightly off, from the concrete, bunker-like bedrooms, to the occasional power outages and the militaristic security methods. Caleb is never at ease and, as the audience’s window into this strange world, neither are we.

A big reason for that is Nathan. Sure, the dorky Caleb is supposed to be intellectually disarmed by the fact that Nathan created the world’s most powerful search engine as a teenager. But Isaac, with his shaved head, thick black beard and burly but fit physique, is an intimidating physical presence as well. He’s a bruiser, a genius, and a charismatic eccentric who spends his days boxing and his nights getting blind drunk alone.

Isaac, who is quickly proving himself to be one of the greats of his generation, plays Nathan as a celebrity of sorts — the kind who is always requesting that the other person just be more “real,” which usually has the opposite effect.

But it’s really Ava’s film. Her form, too, is distracting. Her body, made of caged metal and fiber optics, though interesting and perfectly curved, is secondary to the face — the only visually human aspect to her.

Her innocent beauty, perfect expressiveness, and surprising wit even make Caleb question whether Nathan is using her loveliness to muddle judgment (i.e. the magician’s assistant).

“Did you program her to flirt with me?” Caleb asks self-consciously at one point.

As the test progresses and Ava starts to resemble not an experiment but a prisoner, things get more complicated and motives, all around, become fuzzier. Then, “Ex Machina” elegantly transitions away from a theatrical exercise in discourse into a tense thriller with gripping twists and haunting turns right up to the conclusion.

Perverse and provocative, “Ex Machina” is a cult classic in the making.