You could hardly ask for a more metaphorically striking and economical conceit than the one that motors—literally—Bong Joon’ho’s Snowpiercer. In this post-apocalyptic, ecological thriller, a barely surviving remnant of humanity ceaselessly travels on a high-speed train on which class divisions are both stark and brutally maintained by storm troopers.

In the train’s rear cars are the “tail passengers,” enduring an abject, primitive existence, their only sustenance a black, rubbery protein bar, whose manufactured origins, it transpires, are disgusting. This huddled, repressed population comprises much of what very little is left of humanity after it almost entirely perished in an ecological catastrophe. To correct global warming, scientists accidentally froze the planet through the release of something called C-Z. One instance of the movie’s sometimes arresting imagery occurs when some train passengers view the moving panorama of a spectral, frozen cityscape speeding by. (The often compelling production design is by Ondrej Nekvasil.)

At the train’s front is “the engine” and the mystique-enshrouded maximum leader, Wilford, whose will and edicts are imposed by the armed force and a weirdly didactic and fascistic minister, played by a grotesque, bucktoothed Tilda Swinton, a little show in herself.

The movie’s plot thrust is the revolt of these sans culottes, led by a reluctant guy (Captain America’s Chris Evans), and their savagely violent car-by-car advance on the engine. This results not only in bloody battles won and lost, but in a number of revelations about this supposedly mobile microcosm of humanity, including individual backstories and facts about the train’s operation. But not really enough. Snowpiercer has to be more or less taken on its own terms, and they don’t always make complete sense, even within the conceit.

How these people came to be on this train, and why they seem to be Americans, with a couple of key Asians, aren’t addressed for instance. Nor, really, is the supposed function of this underclass. It doesn’t seem to be a value-producing proletariat—Marxist-wise—laboring to support the luxury-enjoying bourgeois at the train’s other end. And Snowpiercer’s explosive ending is symbolically muddled.

There are hints here and there of Joon-ho’s mordantly distanced, not altogether unsympathetic attitude in his Mother (2009), but this one is extravagantly different. It’s quite a ride, quite unlike just about any other movie in memory.

Opens Friday at the Amherst and Eastern Hills Mall theaters

Watch the trailer for Snowpiercer