Set in a world that is tidally locked, thus one side of the planet is always

Set in a world that is tidally locked, thus one side of the planet is always in light, and the other in darkness. Science rules on the dayside, while magic holds sway in the night. Powerful magical entities live on the night side of the planet, and for the most part the entities' magical powers emanate from distinct loci. Jack of Shadows (a.k.a. Shadowjack), the main character, is unique among the magical beings in that he draws his power not from a physical location but from shadow itself. He is nearly incapacitated in complete light or complete darkness, but given access to even a small area of shadow, his potency is unmatched. Jack's only friend, the creature Morningstar, is punished by being trapped in stone at the edge of the night, to be released when dawn comes. His torso and head protrude from the rock, and he awaits the sun that will never rise. Jack seeks "The Key That Was Lost", Kolwynia. The Key itself and the consequences of its use parallel Jack's progress in his own endeavors. Ultimately, the Key will be responsible for Jack's salvation and his doom. Fleeing the dark side, Jack gets access to a computer and uses it to recover Kolwynia. This makes him unbeatable, but not all-powerful. Having made a mess of ruling with his new powers, he seeks the advice of Morningstar, who advises him to destroy The Machine at the Heart of the World, which maintains the world's stability, and set it rotating. The novel ends with Jack falling, perhaps to his death, but Morningstar has been freed by the world's turning and rushes to rescue him. The fate of this ambiguous hero is left untold, with Jack wondering, as he falls, if Morningstar will reach him in time.