Before the beginning of history, a large cataclysm broke God's divine creation, separating it into multiple dimensions. Human beings live in one of these worlds, a forsaken, over-urbanized landscape, which connects to another environment in some points where the veil of reality is fragile.
The world-besides-ours is called the Frontier, and it is inhabited by sapient larval creatures involved in mystical and dangerous projects. These things full of claws and mandibles have nothing but disdain for humanity.
In daily life, humans try to avoid the Frontier. Until a messiah comes, and everything changes.