As the remnants of human civilization circle a frozen earth on board a massive train, Andre Layton is recruited to solve a grisly murder -- while his friends in the lower classes plot to unleash a violent rebellion.

As the failed rebellion results in mass punishments, Melanie orders the train to press quickly through a dangerous series of avalanches. Andre's investigation reunites him with the woman he loves, and a new crisis in the cattle car threatens the train's future.

As Layton and Till follow a clue into Snowpiercer's seedy black market, Melanie stages a prize fight to distract the passengers from rising tension between the classes.

After another murder on board Layton's investigation leads him to a confrontation in first class, while Till pursues a suspect. The tail comes into possession of a first-class key, and Josie Wellstead tests to see how far it will take her.

When a killer is put on trial for a string of murders, Melanie is pressured to all Second and Third Classes equal representation on the jury. Meanwhile Josie searches for Layton, who is experiencing nightmares about his past in the tail.

Third Class plots a work stoppage in response to the trial results, forcing Melanie to lay down an ultimatum -- until an engineering emergency throws Snowpiercer into crisis. Oz tries to leverage Brakeman Till, and Layton lies low ... until he sees an opportunity.

Miles' appointment as an engineering apprentice draws out Josie, who tries to make contact with him. Layton tries to recruit Third Class passengers into the Tail's revolution, and Ruth goes on an unexpected date.

A peek inside the train's engine prompts First Class to confront Melanie over the secret she has been keeping. While she contemplates her next move, Layton returns to the Tail to lead a revolution.

As Melanie faces execution and the Tailies regroup in Third Class, First squabbles over how to proceed next -- and Pike tries to convince Layton to hand himself over.

In the aftermath of the revolution Snowpiercer Layton takes on a new role, and Melanie faces her personal demons. But as the passengers get accustomed to the new world order, a surprising new foe threatens the train from without.