When thirteen-year-old Gerald finds himself the heir to twenty billion pounds from an aunt he never met, he inherits with it a mystery surrounding his aunt's death and various artifacts in the British Museum.

Amy and Dan Cahill are no strangers to impossible tasks. After seven of their relatives were kidnapped, the siblings scoured Europe for the priceless artifacts Vesper One demanded in exchange for the hostages. But then the Cahill kids are given an assignment that pushes them to their breaking point, a journey to a legendary city. Amy and Dan know they can't afford to fail, yet they're running out of options and running out of time.