It's not very fulfilling being a lowly Supply Technician on the voyaging cityship of World. But when Ben is offered a place at The Exchange, the illustrious and secretive highest caste on the ship, he learns about what can be bought, and what can be sold.

Together with a principled genius and a feckless hacker-mercenary, Ben will have to turn his back on everything he knows to do what's right - and to survive.