Nine months after Snowpiercer and Big Alice parted ways, Till and Ben encounter unforeseen enemies when Melanie sends them off the train on a reconnaissance mission. Meanwhile, the residents of New Eden face uncertain times and unknown adversaries, compelling them to further confront the complexities of their new reality.

Milius and his Animal Squad storm the train. Melanie realizes something is wrong and shuts the vault doors to the engine. But when Ben's life is threatened, Melanie surrenders the engine.

Layton demands to use Big Alice to rescue Liana; Ruth, now mayor of New Eden, refuses because it's the town's power supply; Layton makes Javi jury-rig a solution, giving them three weeks of electricity.

Big Alice catches up to Snowpiercer; Milius radios them, inviting Layton over; sensing a trap, Layton and Josie sneak onto Snowpiercer; Nima is worried Layton will be gassed and attempts to disarm the Greenhouse Car.

Layton hears the deal: Liana for Big Alice. He agrees and the trains dock at the silo. While Layton, Ben, Till, Ruth, and Alex stew in a holding room, Josie is taken to Headwood. Milius introduces his partner in crime: Wilford.

Nima needs more samples for his experiments, so Milius sends Wilford and the soldiers to collect; privately, Milius tells Wolf tohug Wilford; Layton wakes up on an abandoned floor and is approached by humans with toxic gas scars.

Layton learns who was responsible for the experiments on Josie and Liana, before also finding out who froze the world; Big Alice approaches New Eden but can't cross the booby-trapped bridge.

The bridge is safe to cross and Big Alice pulls into New Eden. Layton, Josie, and Liana sit stranded in the middle of nowhere, freezing to passing, when a masked soldier appears.

Alex sabotages the track switch computer and, with Layton's help, escapes to town hall; Till gets the drop on Ace and uses his sniper rifle to save Layton and Alex from Rat; Melanie reveals the identity of Alex's biological father.

Nima heads for Snowpiercer; Layton and the Tailies fight their way uptrain when Ruth is captured; Nima tries to cut a deal and runs to the rocket control room to initiate the launch sequence.