The game follows Reid Hershel as he tries to prevent the Grand Fall, a cataclysmic event that would destroy his planet along with that of newly found traveling companion Meredy. Specifically, the Grand Fall entails the violent collision of twin planets Inferia and Celestia. The two planets, face one another, separated by the Orbus Barrier. Interaction between the two planets has been infrequent over the last few centuries despite their proximity; the Bridge of Light linked Inferia and Celestia in the distant past, but the link has been severed for an extensive period of time. The Aurora War, an ancient conflict that set Inferia against Celestia over two thousand years ago, continues to generate persistent mistrust between the two groups. The Orbus Barrier has shown recent signs of weakening and possible collapse due to the actions of an unknown external force.

The journey takes Reid across both planets, as he seeks out those responsible for this movement towards the brink of annihilation.