In St. Louis, Missouri, Baxter “Bax” Allen is a sophomore at Truman High School. His parents split up 13 years ago, and he lives with his mother, Sara, who supports them with two jobs. He also suffers from episodes in which stress causes him to faint. One night, on his way back from his best friend Jason Franklin’s house, Bax meets a stranger who insists that Bax give Greg, the teen’s estranged father, a gaudy ring with a purple gem. Bax accepts it even though he doesn’t know where his dad is. The next day, as Bax and Jason examine the ring, a short, monkeylike being with white fur appears and asks to be of service. This is Janni, a low-level djinn; it obeys Bax’s wishes, but its powers have limits—for example, it can’t change people in any way. Later, Ashley Bryant, Bax’s brainy neighbor, asks Bax to have Janni spy on her parents. Eventually, Bax dreams of getting everything he wants—financial stability, his parents reunited, and the attention of his crush, Scarlet Lane. However, a more powerful entity may cause Bax to regret his desires. Sullivan presents several familiar ingredients of YA adventures, including a nerdy, underdog protagonist and threatening bullies, but it’s the djinn that truly makes this fantasy shine. Janni provides a fertile source of humor, as when it tries to help with the dishes; it’s also noted that the djinn smells like burnt hair whenever traveling via magic. There’s discussion of how a more powerful djinn could improve the world by, for example, curing cancer, which sounds a note of seriousness to the narrative. Later, well-executed twists ratchet up the horror: “He yelled but only heard the shrill grinding of metal. Then, in a split second, he heard nothing at all.” Bax’s supporting cast is well developed—especially Ashley, who begins the tale as a social outcast. Sullivan provides a tight finale, although fans will surely crave more.