It's been 99 years since Yellowstone park erupted, causing a mass extinction and plunging the world into an ice age. Survivors are living in a structure dubbed the Greenhouse. They believe they're the only survivors, until a message appears on the outside of the glass.
Jack Paul lives in a land of ice and snow, and Ruby Hammond lives in a lush, tropical world where the sun always shines. Even though they're from such different world, their fates are so intertwined that they are destined to meet.