After the apocalypse, Earth stops expanding outward—and begins growing upward.
Trees stretch hundreds of kilometers into the sky. Animals evolve to live at different atmospheric levels, while humanity survives only near the ground.
Then a giant seed falls from the clouds.
Inside is a human city.
Not from the future.
From above.
As survivors climb toward the highest levels of the world, they discover forgotten civilizations, intelligent trees, changing gravity, and a sky that may be the new ocean.
At the top, two human worlds finally meet.