Laura and Billy are all-American expat kids living in London with their parents. Charming eleven-year-old Billy wants to be an entrepreneur and is making a good start with his paper route and by selling American macaroni-and-cheese to his British friends. Pretty teenaged Laura is so boy-crazy she hopes her unique crush-ranking system will be attractive to college admissions boards. But their carefree lives change forever when Billy is handed a mysterious package in a London Underground station.