While Wilford maintains a tight grip over Snowpiercer, the resistance continues to bide their time in secret throughout the train. Elsewhere Layton's pirate train circles the globe to study warm spots.
While Layton's train welcomes an outsider, Wilford tests a new weapon. Snowpiercer prepares to host a wedding to boost morale, and the resistance tries to reach out to Javi.
The return of the pirate train prompts Wilford to rally the troops for the impending conflict, including turning the screws on those collaborating with the resistance. After a setback, Layton looks for an opportunity to get back on board the train.
While helping Ben to clear an obstruction on the track, Alex is haunted by the presence of her mother – and must come to terms with the horrors Wilford has perpetrated to keep her alive. Pike, Roche, and others on the train struggle to adjust to their new situation.
With the train hopeful about the future Zarah goes into labor, and Layton is distracted by an apparent arson attack up train. Josie deals with side-effects of her cold treatments, and Ruth and Pike consider whether they should be together.
Till's investigation of the bombing leads to Pike, forcing Layton to lead a manhunt to find his former friend. Sam Roche's loved ones try to bring him back into the light.
While Layton lies in a coma, his mind travels through an alternate version of the train – where enemies are allies and everyone is playing different parts. Till asks Audrey for help in getting through to Andre.
After Mr. Wilford suggests that Melanie might be alive the train changes course, only to come face-to-face with a deadly environmental catastrophe on the track ahead.
The train makes a daring attempt to rescue Melanie from a bullet train, leading to hopeful reunions and a train-wide celebration as "New Eden" draws near. But as alliances shift, new lines are drawn on Snowpiercer.
Melanie's return thrusts the train back into conflict, with doubt cast on New Eden and old factions realigning for war – as Melanie strikes a deal with the Devil.
