The novel is set on a planet that does not rotate, so that half of it is in perpetual darkness and half has perpetual daylight. Born in Twilight, Jack of Shadows is soulless, like a darksider, and has a finite number of resurrections. He is unfairly executed for a crime he had not yet committed and is sent to the Dung Pits of Glyve to begin another life. He awakes in the Dung Pits and begins his return.
Unlike other darkside magicians, Jack does not have a stable power base, but he is able to gain strength and work magic whenever he is in shadow. Defenseless in the everlasting night near Glyve, Jack meets Old Rosie, a tavern girl from his past who has become a Wise Woman. Despite Rosie’s help, Jack is captured and kept in a magical prison of mirrors and light. Evene, the woman he had hoped to marry, has wed the Lord of Bats and disdains both Jack’s powers and his love for her.
The Lord of Bats attempts to drive Jack mad, and Jack vows vengeance. Jack escapes from his prison and, as he travels toward twilight, he visits his friend, Morningstar, a huge, Promethean angel trapped on a mountain awaiting dawn, which will never come because the planet does not rotate. Jack then journeys to the dayside, where he becomes Jonathan Shade, a sociologist and expert on darkside culture. While at the university, Jack uses a computer to rediscover a lost magical key. Using his newly found powers, Jack conquers the darkside, but Evene refuses to love him until he bespells her. Old Rosie brings Jack his soul, a white egglike rock that appears in his hands whenever he is resurrected. Jack shatters the egg, and his disembodied soul begins to follow him about, nagging him.
Jack competently but ruthlessly rules the darkside until the Shield compact is broken, meaning that his world will freeze unless he can prevent it. He has no choice but to travel to the center of the world and smash the world machine. This results in the planet beginning to rotate. When the sun rises for the first time on Shadowguard, Jack’s powers fail, and Evene, recovering her memory, goes mad. Jack unites with his soul as Morningstar, freed at last, flies to rescue him as he falls from a crumbling tower.