The wreckage of the snowpiercer is covered in ice and snow, and is slowly blending into the barren stark white landscape. The tracks of Yona and Timmy have long since been covered by snow, but the railroad tracks begin to shake the weather clear and we see another train in the distance. A second Wilford supertrain is slowing before the wreckage of the first.

When the train stops, after a long silence, one of the doors of the train opens and a hesitant passenger steps out. Then there are more people, armed forces and first class passengers, their bright clothes visible for miles against the white earth. Then there’s an explosion at the tail end of the long train, and dozens of the tailenders spill out of the broken heap.

When a struggle ensues, we see people slaughtered on both sides of the conflict, while many others flee into the mountains. There’s shouting and gunshots, then silence. The world is quiet again.

6 months later a small group of people are seen huddled in one of the train cars, a combination of living quarters for both humans and livestock. The people are well-clothed, even if the clothes are dirty, and decently fed, though they share the meat from a recently cooked chicken. The dozen people seem to have an uneasy alliance, bickering over possessions and getting into physical fights. When a noise comes from outside, however, they all work in unison to seal the train car off.

They are scared, hiding from raiders who have again come to pillage what food is left aboard the second train. The frightened group says that what the pillagers have come for is likely the last of the food, and from the angry muffled shouts and violent bangs against the metal walls, it seems the raiders are upset by what little left there is to steal. The next time the raiders come, says someone from the group, it will be for the small band of surviving passengers. After the raid is over, they decide they have to leave the train.

They journey over mountains, fighting wolves, harsh storms, and amongst themselves, until they reach what appears to be a small town constructed from the remains of cars, ships, and storage containers. Using reflective surfaces, the people have cleared and heated a patch of earth where they are growing food and raising polar bears for meat, but the town is far from prosperous.

The town cautiously brings them in, and when the townspeople find out they are train survivors, there is infighting over whether or not the group should be allowed to stay. For days, the group is watched, kept away from the children, though one townsman confesses he was a survivor of the first train, part of the rebellion that led to its destruction. He says how weak they were individually, but their collective hatred for the evil, selfish people of the front gave them strength. Sometimes, he says, you need a proper villain to help humanity thrive. As he finishes his story, he begins to realize that this group of trainfolk may not all have been from the tail end.

Before he can confirm this, the raiders show up. The second train group thinks they must have tracked them from the wreck, but a villager meets the raiders, pointing out their new guests. The raiders capture the visitors and travel back to their own base, a massive underground facility complete with electricity and running water. The Wilford Incorporated logo is all over the walls and appears to be a factory and testing facility for the trains that existed prior to earth freezing over.

As the group waits in a holding room, they try to determine if the raiders and the others they met were perhaps also in some way tied to the train, and more importantly, which car sections they were from. If they were from an opposing class of passengers, they could make trouble for the group, so the captives decide not to confess anything about which end of the train they were from.

One by one members of the group are taken away for interrogation as the audience is left to make their own determination as to the origins of everyone. One man who talks escape plans appears to possibly be a former military personnel on the train. A woman who is bothered by just about everything comes across as one of the former privileged. An older man, frail, but generous and caring, just wants them all to live through this new struggle. A young couple, neutral in their behavior, are determined to stay together. In the end, we don’t know which section any one of them was from, only that they learned to survive together.

Each person comes back from their interrogation telling of one-armed man who drilled them for answers, while an Asian girl stood by his side, staring. When the prissy woman doesn’t return from her interrogation, the group is taken from holding and shown their work areas and living quarters. It is clear that they will be staying against their will. The old man, however, is taken from the group weeping. They assume he’s seen as a useless commodity and will likely be killed.

The couple and the others begin work on an assembly line. They have a daily routine and they work alongside others who have come from different parts of the world, either stumbling into the raiders on patrol or taken from villages and towns they had established. We discover that the raiders are taking resources wherever they find them and bringing them back to the base for their own use, and having the workers construct new trains so they can expand their global reach.

The couple works the assembly line, the tough military guy is recruited as a guard, the prissy woman is a cleaner. Among the workers there are struggles, and a gang-like pecking order. It’s prison life where too many people have forced groups to form to survive. Not all the workers are able to make it in that life. Some are murdered by their own, and when someone attempts to run, they are publicly slaughtered by the leader’s men.

Others cling to existence, as sad as it may be. Life here is better than on the train, as some say, but others wish for more. They all agree that if they want to choose what life they want, they would need to leave the old Wilford base. The couple, the cleaner, and the guard work together and form an escape plan.

When their plan fails, it is revealed that Yona, the Asian girl with clairvoyant powers, saw what they were going to do and told their leader, the one armed man. He gathers the entire base and executes the guard and the prissy cleaning woman. Yona is clearly upset by the event, and its evident she has been physically and emotionally beaten down, but only steps in when the leader calls for the young couple to be executed as well. Yona convinces him instead to put them in the breeding program where they are producing the next generation of loyal servants. The young man becomes an assistant with injecting women to impregnate them, and the young woman is one of the women tasked with carrying children.

The leader, in Genghis Kahn style, comes in weekly to donate his sperm for the breeding, and we know now that all the babies are his, and in many cases he rapes the women rather than relying on scientific methods.

Time passes. The young woman becomes pregnant, and the couple isn’t entirely sure who the father is. Witnessing his partner’s rape time and again, the young man wants to kill the leader, but the young woman wants to escape. The rebellious couple finds an unlikely ally in Yona. She lets them know their baby will become important for the new world. She wants to help them escape on a recently completed train, but says she’ll stay behind to kill the leader so the raiders won’t be forced to hunt the couple down.

Through a time lapse we watch the young couple’s baby grow up on a farm, become leader of a community. Then that community wars with the neighboring town. As time passes, it is apparent the boy is ruthless and terrible, starting a war with the disparate survivors of humanity.

Yona narrates to explain that this war would bring the small towns together to defeat him, which ultimately combined their resources to better expand humanity and extend the viability of human survival. In the last part of the montage we see an older Yona killing the couple’s son, thousands of people gathered in celebration.