Humans are fascinated by the wonders of space. We know so much about Mars, but what's underneath our very feet? Aspen is a teenage boy on the brink of entering adulthood when he falls in a hole on the way home and finds himself somehow alive 70 kilometres below ground, in a mysterious area called the Subterrane. He must embark on a perilous journey throughout the catacombs of the Subterrane to make it home.