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

The rebel forces are on their heels when a dangerous foe joins them. A plan is hatched to take the train, but it may destroy them all.

On a divided Snowpiercer, Melanie intensifies her search for Layton while Layton is weaponizing her secret. Third Class faces a reckoning when he presents them with a choice.

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