Starring Tilda Swinton and a perpetual-motion machine.

What is it about trains and class warfare in science fiction? Ayn Rand's Atlas Shrugged, about a railroad magnate who joins the rest of the 1 percent on a strike to protest the 99 percent's whining about income inequality, has a chugging train at its heart—Rand points to trains as a symbol of everything humanity can aspire to be. Bong Joon-ho's Snowpiercer takes its name from the futuristic super-train in which everyone left on earth lives—the film introduces the train as the "rattling ark" that's keeping humanity alive. This train, too, represents a kind of Randian dream: In the middle of the 21st century, the grubby masses are forced to live in the rear cars, in near-darkness and the filth that comes from putting too many humans in a too-small box. The wealthy few live in the luxurious, sprawling cars at the front, and the 99 percent are kept in line with threats, reminders that things are exactly as they should be, and an imposing cadre of armed, paramilitary types.

This world died not with global warming, but in ice; a last-ditch effort to curb rising temperatures with an airborne cooling agent called CW7 resulted in the entire world freezing to inhospitable temperatures (CW7 must be a close cousin to Ice-nine from Kurt Vonnegut's novel Cat's Cradle). Only the Snowpiercer, a perpetual-motion machine of a train on tracks that stretch across the entire world, survives. It's a lunatic premise, but Snowpiercer manages to get everything exactly right. This is a world-class science fiction movie, an ambitious, overstuffed epic that will influence young directors for years to come.

The secret to Snowpiercer's success? In a word: commitment. Bong treats the premise with the same respect that he gave to his incredible 2006 creature feature The Host. Not every director could make a movie that takes place entirely in the rectangular boxes of a train and still make that film visually interesting all the way through. The early scenes are so dark that you'll have to squint to make out the action, but as the huddled masses work their way to the front of the train through remarkable acts of violence, each new car develops its own visual palette, a kind of Dante's Inferno—or is it more Wizard of Oz?—quest through the strata of society.

The cast follows Bong's lead. Chris Evans, as Curtis, plans the uprising and serves as the Captain America–like spearhead for the assault on the wealthy, but he also harbors some ugly darkness. Tilda Swinton's Mason is the mouthpiece of the 1 percent, the person in the unenviable position of telling the poor people at the back of the car that they're required to eat nothing but nauseating gelatinous protein bars because the universe wants rich people to eat steak. She plays Mason as impossibly broad, a living, sniveling cartoon, but somehow through the layers of makeup and false teeth making her face into a caricature, and her Thatcherian Yorkshire accent, she helps make everything around her more realistic.

Many critics will probably intend to praise Snowpiercer by saying that it doesn't beat its viewers over their heads with its politics. Those critics are wrong; this is an entirely political movie. Though it's based on a French comic book from the 1980s, Snowpiercer is entirely about class war, and income inequality, and all the most pressing political issues of our time. This train is chugging down the same tracks as Atlas Shrugged, but in the opposite direction. One day, the two are going to collide. recommended