After a catastrophic freeze sweeps across the world, Anna and her five-year-old daughter Emma are locked out of the shelter Anna designed by her husband Nick and best friend Mia, leaving them to die in the blizzard.
Reborn before the apocalypse, Anna abandons the idea of a fixed shelter and transforms a heavy train into ARK-01, a mobile doomsday fortress. When the deadly freeze arrives, she travels through the frozen world with Emma and rescues Ethan, a former railway engineer who becomes essential to keeping the train running—and eventually becomes family.
Meanwhile, Nick and Mia lose their shelter and supplies and become obsessed with taking ARK-01 for themselves. Their attacks escalate from blocking the tracks and ramming the train to explosives and armed assaults. Through the brutal cold and relentless pursuit, Anna keeps ARK-01 moving toward the southern safe zone, determined to give Emma what she couldn't in her previous life—a home that can always keep moving.
