A grisly murder stokes class division on Snowpiercer, the Great Ark Train. Melanie Cavill, the powerful head of hospitality, deputizes a dangerous rebel to help solve the killing -- Andre Layton, the world's only surviving homicide detective.

Layton descends into the black market with Till, searching for both the killer and a valuable commodity for his revolution. Melanie stages a prize fight to distract the passengers from mounting class tension.

Tensions between Third Class and First Class are boiling as Melanie stages the trial of the Snowpiercer killer. Third Class threatens a work stoppage, demanding representation on the jury, and Melanie makes a fateful decision about which side to favor.

In the revolution's aftermath, Layton and Melanie realize the greatest threat to their survival is right over their shoulder.

Mr. Wilford arrives and threatens Snowpiercer, so Melanie makes a move that can't be undone.

An exchange is made between the two trains, but a far greater revelation might be just over the horizon.

Melanie embarks on her most dangerous mission yet, while Layton reckons with his personal choices.

Layton and Miss Audrey make a risky play for Big Alice, but Wilford has his own plans.

Layton and Till investigate the murders. Wilford leads Miss Audrey down a dark path.

Wilford presses forward on his endgame while those who are close with Layton grow anxious to learn their fates; Josie tests her newfound ability.

Alex must finally deal with her parental figures as a track obstruction uncovers a painful past.

A series of terrorist attacks threatens to derail Layton and Zarah's big day.

Reunited with old friends, the train throws a party. Alliances are tested as the truth is finally revealed.

It all comes to a head as old adversaries clash, with New Eden hanging in the balance.

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.

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 to kill Wilford. Layton wakes up on an abandoned floor and is approached by humans with toxic gas scars.

Big Alice pulls into New Eden. Layton, Josie, and Liana sit stranded in the middle of nowhere, freezing to death, when a masked soldier appears. Can he rescue them? Alex finds herself in danger.

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, but who is trying to sabotage the rocket?