An endless expanse of snow covers the world, with no sign of stopping its expansion. The people who live in this world are able to survive by either staying near the roots of massive trees scattered throughout or inhabiting the planet's atmosphere in the canopy high above. Kaina, a teenage resident of the canopy, and Liliha, a young woman from the surface, have a fortuitous meeting that sets in motion a series of events that change the fate of the world.