The titular Jack is a Nightside dweller, but one with a unique quirk - instead of having his power bound to a specific location like everyone else, it is drawn from the shadow itself. This means that he is helpless in daylight or in pure darkness (since shadows are cast by the light), but enormously powerful once he finds any shadow to nest in.
This novella features examples of:
- Absence Makes the Heart Go Yonder: At the beginning of the novel, Jack was intending to steal a priceless gem as the price for marrying his beloved Evene. After he is captured and executed, he returns to life some number of years later, and after a time he's captured by the Lord of Bats and imprisoned for a further time in a crystal prison. During this time, the Lord of Bats obtained the gem legitimately and proposed to Evene, telling her that Jack had abandoned her.
- Always Night: The Nightside, the half of the planet that is always facing away from the sun.
- Badass Boast: "I am Jack of Shadows! Shadowjack the Thief! I was beheaded in Igles and rose again in the Dung Pits of Glyve. I duped the lord of High Dudgeon in his keep and took his prize and pride. I am the prisoner in the jewel. I am the breaker of the Compact. I drank the blood of a vampire and ate a stone. So beware, all those who love the Lord of Bats or loathe me, for I have named myself Jack of Shadows!"
- Being Tortured Makes You Evil: Jack had a small and tidy list for revenge, against people who can return from the dead and play these kind of death games regularly. Then the Lord of Bats traps Jack in a crystal designed to counter his every trick with the expressed intent of driving him mad. It's this time that made him decide to seek the Key That Was Lost and use it to conquer the entirety of Nightside.
- Jack fears this with Evene, he comes to regret brainwashing her into loving him again, but won't release it because he knows she'll hate him and expects her to go mad.
- Best Served Cold: Jack's revenge is a long time in coming.
- Better to Die than Be Killed: On his revenge tour, Jack visits the Colonel Who Never Died. After they chat and reminisce for a while, Jack frankly says that the Colonel will have to die, but due to their past friendship he will let the Colonel kill himself. The Colonel is deeply thankful for this, especially because it lets him keep his record of never being killed by another Darksider.
- Dark Is Evil / Dark Is Not Evil: It's a relative thing. Jack is a pretty bad guy from the beginning, but there is a significant difference between the Jack of Shadows and the man they call "Jack of Evil".
- Demon Lords and Archdevils: Jack finally deduces Morningstar's probable identity near the end of the book.
- Disney Villain Death / Bolivian Army Ending: At the end, Jack's keep is destroyed as his power is thwarted, and Jack is thrown from a tower. The last thing he sees is Morningstar flying towards him, arms outstretched to catch him, and Jack wondering if he'd make it in time.
- Eternal Engine: There is a Machine at the Heart of the World (the purpose of which is to stop the Earth from rotating).
- Evil Overlord: A fair approximation of what Jack becomes.
- Good Smoking, Evil Smoking: Jack picks up the habit dayside.
- Impossible Task: Stealing the Hellflame for Evene's bride-price.
- In the Hood: Jack wears one.
- Irony: Jack escapes his imprisonment by the Lord of Bats by forging his name on the Compact as current protector of the Shield. He notes that his opponent was the true guardian, and that if either of them had been minding their actual business, none of the plot would have happened.
- Mayfly–December Romance: Jack and Rosalie. He promised to come back for her...and does—an unspecified number of decades later, long after she has grown old and begun to resent the fact.
- Mind Rape: Jack's revenge on Evene for marrying the Lord of Bats is to brainwash her into loving him again.
- My God, What Have I Done?: Jack does realize that what he has done to Evene is unpardonable—but he fears to undo it, as being freed would drive her utterly insane.
- Naked on Revival: Anyone who is resurrected in the Dung Pits of Glyve.
- Perfectly Arranged Marriage: Evene to the Lord of Bats...eventually.
- Pet the Dog: Jack tries to do this with Rosie. He can't quite get the hang of it, however.
- Respawn Point: If anyone gets killed before exhausting his finite supply of lives, he is resurrected in the Dung Pits of Glyve at the east pole of the planet.
- Revenge: Becomes Jack's driving motive... in the interim.
- Roaring Rampage of Revenge: A low-key one when Jack finds of Rosalie's death.
- Shadow Walker: This is one of Jack's signature abilities.
- Speak of the Devil: Jack's powers include the ability to hear any person who speaks his name in shadow, and to continue listening in until they move out of it.
- Sue Donym: Jack of Shadows becomes "Professor John Shade" on the Dayside.
- Villain Protagonist: Jack. He's never the nicest person to begin with but once he sets out for revenge he casts out almost all semblance of morality.
