For Khadija, the only escape from her father's arranged betrothal is the sky. When she spots a rogue hot air balloon fighting against its ropes, she leaps at the chance for adventure. Khadija soon finds an unlikely ally in a poor glassmaker's apprentice, Jacob.

But Jacob is a hari, and Khadija a Ghadaean. The hari are oppressed and restless - their infamous terrorist group, the Hareef, have a new fearsome leader. And the ruling Ghadaeans are brutal in their repression.

Soon, a deadly revolution threatens their friendship and their world. The Hareef use forbidden magic, summoning jinn - wicked spirits made of fire - to enact their revenge, forcing Jacob and Khadija to choose what kind of a world they want to save ...