A human soul is stuffed into King Sombra's body. Having no idea what's going on, and thinking he is in some kind of coma, he just casually strolls into the Crystal Empire.
Sequel to The Celestia Code. When the monsters created by the dark crystal engine escape their prison, it's up to Princess Twilight to deal with them. She gets help and advice from Princess Luna, but things don't go as planned.