In Bong Joon-ho’s highly anticipated Snowpiercer, the last fragments of humanity survive aboard a massive train that navigates the globe once a year. Outside the train, the world is an uninhabitable frozen wasteland following a botched attempt to lower the world’s average temperature in the face of global warming. Inside, a fragile socioeconomic system keeps the have-nots in the train’s dingy caboose, while the elite exist in luxury, spending their time in the train’s night club, aquarium, and other opulent cars. This recipe leads to a truly great, overtly political sci-fi film that feels like a summer blockbuster, but is just weird and visionary enough to transcend the season of big budget trash.

The titular train was created by a mysterious man named Wilford, a sort of neo-Marxist Wizard of Oz. The locomotive is Wilford’s self-sustaining empire, where society has essentially continued as it was pre-ice age. The train’s elite keep the have-nots in the rear under their thumb by controlling their resources, barely keeping them alive on “protein blocks” that resemble rotten Jell-o. They impose poverty and manipulate food supplies to ensure complete conformity is sustained. And Captain America ain’t having that.

Chris Evans plays Curtis, a have-not plotting a rebellion with his buddy Edgar (Jamie Bell). They’re counseled by Gilliam (John Hurt, who can still effortlessly steal a scene at 74-years-old). During the course of their rebellion, they’re joined by security expert Namgoong Minsoo (the great Song Kang-ho) and his daughter Yona (Ko Ah-sung), both drug addicts. While Wilford remains behind the curtain, his lead crony Mason makes sure that everyone “Keeps their place.” Mason is played by Tilda Swinton, who is damn near unrecognizable in the role. She’s clearly channeling Margaret Thatcher, whose moral compass always seemed to be on the fritz. With her teeth, her hair, her thick Yorkshire accent, Swinton gleefully transforms into what I’m certain will turn out to be one of the best villains of the year.

As grand as her performance is, Swinton does come dangerously close to going over-the-top. She balances the absurd elements nicely though and the true excessiveness is left for Alison Pil, who plays a schoolteacher with a fondness for uzis and propaganda. The entire film, in fact, rests on this tenuous balance of ridiculous and solemn. As Curtis and his crew of revolutionaries push their way to the front of the train, they encounter an unpredictable series of baddies and obstacles, resulting in some gloriously staged fight sequences.

Snowpiercer is all about momentum and Bong deftly maintains it, knowing when to keep the pace booming along and when to slow down the drama for maximum effect. The production design on this film is tremendous, so during these moments when Bong hits the brakes a little, there’s a lot to soak in. It’s wise to slow down the action at times as well because Snowpiercer is filled with shocking revelations and twists the audience is going to want to thoroughly digest.

At its best, science fiction addresses the problems of today and that’s exactly what Bong’s film does. It can feel heavy-handed at times, but there’s a thoughtfulness and sincere anger at Snowpiercer‘s heart that makes it an intoxicating blend of class violence and big ideas. And like the contemporary issues in our society, the film offers up no simple solutions, just more troubling questions.