Plot

In a future where a failed climate change experiment has killed all life except for the survivors who boarded the Snowpiercer (a train that travels around the globe), a new class system emerges.

Set in 2031, the entire world is frozen except for those aboard the Snowpiercer. For seventeen years, the world's survivors are on a train hurtling around the globe creating their own economy and class system. Led by Curtis (Chris Evans), a group of lower-class citizens living in squalor at the back of the train are determined to get to the front of the train and spread the wealth around. Each section of the train holds new surprises for the group who have to battle their way through. A revolution is underway.—Anne Campbell

The nations release the substance CW-7 with the intention of controlling global warming, but accidentally it results in another Ice Age destroying Earth. The only survivors live in the train Snowpiercer which is driven by a perpetual motion engine created by the millionaire Wilford (Ed Harris) that lives in the engine part. In 2031, after seventeen years, there is a fight of classes inside the train since the oppressed lower class lives in dreadful conditions in the last wagons of the train while the elite lives in the front wagons. The lower class is fed with protein bars only; they are oppressed and punished by Minister Mason (Tilda Swinton) and her brutal guards; and their children are taken every now and then when they reach a certain height. The leaders Gilliam (Sir John Hurt), Curtis Everett (Chris Evans), and Edgar (Jamie Bell) are plotting a scheme to reach the engine and talk to Wilford about their conditions using the addicted security engineer Namgoong Minsoo (Song Kang-ho) and his clairvoyant daughter Yona (Ko Asung) that are imprisoned to open the locked doors. When the son of Tanya (Octavia Spencer), Tim (Marcanthonee Reis), is captured by Mason, they decide to execute their plan. There are many casualties and soon Curtis discovers that they have been manipulated by Wilford to balance the resources in the train, and why the magnate keeps the lower class alive.—Claudio Carvalho, Rio de Janeiro, Brazil

It's 2031, seventeen years after authorities in seventy-nine countries decided collectively to combat global warming with the coolant CW-7. The result was the Earth being immediately sent into a deep freeze, killing all human life except a handful who now live on an "ark", a revolutionary train built before 2014 by a train aficionado named Wilford (Ed Harris), the train which at that time was considered useless and self-indulgent. The train is required to be constantly moving to generate energy for life inside, it which circumnavigates the globe on a single continuous track once every year. The train is still controlled in all of its aspects by Wilford, who has created three separate classes housed in different parts of the train: the privileged "one percent", who are at the front of the train, the workers who support both ends and occupy the middle of the train, and the "tail people", the masses who live at the back of the train like cattle in a windowless cattle car, they being solely fed protein bars, whose ingredients the tail people do not know. The face of Wilford's ideology to those in the tail end is Minister Mason (Tilda Swinton), as Wilford never ventures to that end of the train. Some of the policies which Wilford has implemented is taking many of the children from the tail end for an unknown purpose never to be seen by the people in the tail end again, and committing occasional indiscriminate genocide in the tail end, most of the tail people believing as a method of population control, and to demonstrate his dictatorial power in an effort to have a complacent populace amongst the masses. There have been many attempts of revolution by the tail people in the past, all quashed by Wilford. Curtis (Chris Evans), one of the tail people, wants to attempt another revolution, he believing all past attempts having failed because they have focused on Wilford, as opposed to what he feels needs to occur for power: take control of the engine at the front. Supporting Curtis in this fight are, amongst others: Gilliam (Sir John Hurt), the wise old man; Edgar (Jamie Bell), who Curtis took under his wing when he became orphaned in the early years; and Tanya (Octavia Spencer) and Andrew (Ewen Bremner), who want to find their children taken away. Along the way, they have to co-opt Namgoong Minsoo (Song Kang-ho), an addict of a synthetic hallucinogen called Kronole, he who designed the security system, namely the locking mechanism of the gates between all the train cars. As Curtis and his team try to work their way from car to car from the tail to the front, their priorities are influenced by what they see, what they learn, and by revelations including secrets from their individual pasts.—Huggo

In 2014, the world attempts to counteract global warming through stratospheric aerosol injection. The technique was developed over the previous 7 years. 79 countries started disbursing the aerosol CW7 with the promise of defeating global warming. CW7 was an artificially developed atmospheric cooling agent designed to bring down temperatures to a more manageable level. However, the experiment catastrophically backfires, creating a new ice age that destroys much of life on Earth.

For 17 years, the remnants of humanity shelter in a state-of-the-art self-sustaining perpetual motion train, the Snowpiercer that travels a circumnavigation-based track, created by the transportation magnate Wilford (Ed Harris).

By 2031, elites inhabit the extravagant front cars, and the "scum" inhabit the tail in squalid and brutal conditions. At first, the order was prescribed by the ticket of the passengers, first class, economy and freeloaders. Now the eternal order is prescribed by the Sacred Engine.

Under watch by Wilford's guards, they are brought only gelatinous protein bars to eat and kept in their place in the social order by Minister Mason (Tilda Swinton), while sometimes small children are taken away under the guise of medical checks, but the kids never return. The tail coaches are attached to the guard coach and beyond those lead the more opulent sections of the train. The tail section is crowded with no privacy for people.

Any sign of disobedience is met with a swift and brutal response from the guards. Punishment includes opening a small portal in the carriage and putting the rebel's arm outside in the freezing air. In 7 minutes, the arm is rock solid after which it is broken off with a sledgehammer. As the hand thaws, the pain returns with infinite agony.

Conspiring with his mentor Gilliam (John Hurt), Curtis Everett (Chris Evans) leads the tail passengers in a revolt that he plans will take them all the way up to the engine. Hidden inside the protein bar, Curtis receives a message with the name of Namgoong, who is in the prison section of the train. Curtis has calculated that the tail section is followed by the quarantine section, followed by the prison section. All 3 sections are protected by gates and there is only a 4 second window when all 3 gates are open at once. Namgoong designed the security features of the train and can get them to the engine. Custis says that all past revolutions failed as they could not get to the engine.

Overpowering the guards, they release security expert Namgoong Minsu (Song Kang-Ho). For his assistance, they bribe him with Kronole, an addictive drug made from industrial waste. Namgoong also insists that his clairvoyant daughter, Yona (Go Ah-Sung), be freed so as to disable the locks between cars.

They take the car where insects are ground up to make their protein bars, and Gilliam suggests that if they take the subsequent water supply car, they will control any negotiation with Wilford.

Instead, they are ambushed by a mass of masked men with hatchets led by Franco the Elder (Vlad Ivanov) under Mason's orders. After a bloody battle Curtis sacrifices his second-in-command Edgar (Jamie Bell) to win the fight. Mason is taken captive and agrees to give free passage to Curtis, Namgoong, Yona, and three other rebels: Gilliam's bodyguard Grey (Luke Pasqualino), Andrew (Ewen Bremner) and Tanya (Octavia Spencer) who have had their respective children Andy and Timmy taken away.

Curtis's group travels through several opulent cars. Namgoong and Yona recognize a landmark outside and speculate that the ice may be thawing more and more with every year. The group reaches a schoolroom, where a teacher is indoctrinating the children on Wilford's greatness. A bald man brings eggs for the children to celebrate the train's eighteenth circumnavigation of the Earth.

Then the bald man goes to the tail army and shoots them with automatic firearms hidden under the eggs. The captured guards are freed, as is Mason's henchman Franco. The teacher, who received a gun from the bald man, kills Andrew before Grey kills her. Franco broadcasts to the classroom his execution of Gilliam, which prompts Curtis to execute Mason in turn. Curtis's group moves on, but Franco catches up with them, killing Grey and Tanya. Franco is then seemingly killed by Curtis and Namgoong.

In the last compartment before the engine, Namgoong reveals that the reason he collected the Kronole was to use it as an explosive to escape the train with Yona, believing they can now survive outside. Curtis explains that in the early days of the train, the tail section resorted to cannibalism. Edgar was an infant when Curtis killed his mother, and Curtis was going to eat him when Gilliam offered his severed arm instead, stopping the bloodshed. Curtis wants to confront Wilford for causing such horrors. Wilford's assistant, Claude (Emma Levie), emerges from behind the engine room door to invite Curtis inside.

Curtis meets Wilford and, to his shock, learns that he and Gilliam conspired to stage Curtis's rebellion to reduce the tail section's population to sustainable levels. After ordering the execution of most of the tail section residents, Wilford offers Curtis his position leading the train. Curtis appears ready to accept as Yona overpowers Claude, rushes in, and asks for a match.

In desperation, she pulls open a floorboard to reveal Tanya's son, Timmy, working the engine as a replacement for a broken machine part; taken from his mother to be a slave. Appalled, Curtis beats up Wilford and rescues Timmy from the machinery; though he loses his arm in the process. Andy, Andrew's missing son, crawls out of a nook and climbs into the engine core despite Curtis's pleas. Curtis gives Yona the match to light the fuse for the Kronole bomb, while Namgoong fights and kills Franco, who followed them. Damaged by the fighting, the door to the engine room cannot be closed, forcing Curtis and Namgoong to use their bodies to protect Yona and Timmy from the blast.

The explosion triggers an avalanche that derails and wrecks the train. Curtis and Namgoong are unresponsive, so Yona and Timmy escape the wreckage. They see a polar bear in the distance, indicating that life exists outside the train and did not die out as they were first led to believe.