Delving into the realm of existential science-fiction, director Jonathan Glazer (“Sexy Beast,” “Birth”) examines what it means to be human.

Accompanied by a shadowy, silent motorcyclist, there’s an expressionless, extraterrestrial stalker (Scarlett Johansson) on a mission.

Driving a white cargo van, this alien femme fatale roams the crowded city streets of Glasgow and the rural Scottish Highlands, wearing a black wig and clad in a fake-fur jacket, torn fishnet stockings and

stiletto heels, prowling for her chosen prey: lonely, unattached men.

When she randomly finds a compliant victim, she offers him a ride, seduces him, strips him and sinks him into an inky, inescapable void. Although murky, there’s some subtext about harvested human fillets being sent back as part of the food chain on her home planet.

Loosely based on a Michael Faber‘s satirical, metaphorical novel, “The Crimson Petal and the White” (2000), it’s adapted as a kind of B-movie horror story by director Jonathan Glazer with Walter Campbell, complete with reminiscent tinges of wraithlike David Bowie in Nicolas Roeg‘s 1976 classic “The Man Who Fell to Earth.”

Fortunately, there’s not much dialogue because Johansson’s British accent is wobbly and the thick brogue spoken by most of her Glaswegian cohorts is indecipherable.

The press notes state that most of the men in the film are non-actors who didn’t realize they were being filmed by small digital cameras concealed in and around the van; it was only after they complied that they were asked to sign a “Candid Camera”-like release.

While atmospheric concept is mysterious and the imagery intriguing at first, repetitious tedium soon sets in, which makes it seem longer than the 108 minute running time.

Credit Johansson for once again embodying an enigmatic entity that men desire, a role she’s played in one form or another in “Girl with a Pearl Earring,” “Lost in Translation” and “Her.”

On the Granger Movie Gauge of 1 to 10, “Under the Skin” a subtly strange, surreal 6, appealing to avant-