Reid Hershel and his companions are racing to prevent the Grand Fall — a catastrophic collision of twin planets that would destroy both worlds at once. Inferia and Celestia orbit each other, kept apart by an energy field called the Orbus Barrier. For most of their shared history the two worlds have had little contact; the Bridge of Light that once connected them broke long ago, and the Aurora War, fought over two thousand years past, left a lasting mistrust on both sides. Now the Orbus Barrier has begun to weaken, destabilized by an unknown external force. Reid's companion Meredy has crossed over from Celestia to warn them, and what she carries is urgency: if the barrier collapses, both planets die. The journey spans both worlds as Reid works to find who is behind the destabilization and stop it before time runs out.