Aura has always known two things: the sky is their home, and the world below is forbidden. She lives in Aerilon, a shining city of sky-steel, filtered air, and humming anti-gravity engines, floating safely above the vast, messy Surface. But when a moment of high-flying curiosity leads to a catastrophic slip, Aura tumbles through the clouds and crash-lands in the one place she was warned never to go.

Now, instead of smooth glass and the taste of ozone, Aura is surrounded by mud, thorn-tangles, and the overwhelming scent of wet, wild earth. Her high-tech suit is useless, her Sky-Glass Compass is fading, and the silence is broken only by the whispers of creatures she can't name. She soon meets Flint, a cautious Lowland boy with dirt on his knees, who shows her a world of forgotten streams, secret Tanglewoods, and the silent, watchful Lowland Guards.

As Aura navigates the dangers of the Surface, she begins to uncover a deeper truth hidden in ancient stone carvings: Aerilon didn't just float away, it abandoned the world below. With the glow of her city growing faint on the horizon, Aura must journey to the towering World’s Old Spine, following the forgotten clues of a Lowland engineer. Her mission is no longer just to get home, but to confront the devastating secret that keeps the two worlds apart. Can one girl from the clouds survive the dangers of the ground, or will the secrets of the Surface bury the truth forever?