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.

Hiding out with help from his allies, Layton lays track for revolution and an engineering emergency threatens every soul on Snowpiercer.

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.

As the Big Alice crew are granted shore leave on Snowpiercer, Layton and Wilford have differing opinions on the future.

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

As the train approaches Melanie's retrieval point, Layton leads a furious attempt to try and pick her up but not without some sacrifices.

While Wilford emphasizes his rule aboard his icy train, Layton's pirate train continues its dangerous quest for warm spots, and comes across something entirely unexpected.

Layton goes on the hunt, as Wilford works to boost morale. The resistance discovers a threat that could undermine everything they've worked for.