At twelve, Li Hua is sold to a floating brothel, but destiny has other plans. Behind the walls of the Forbidden City, she evolves from concubine to spy. She navigates treachery, suppresses a rebellion, and engineers a bold escape with only a mastery of martial arts and a cinnabar dragon pendant imbued with the fatal poison known as GU. In modern-day San Francisco, Lu Carter, an adopted Chinese American and a medical engineer, is introduced to the mysteries of her family's past when she receives an ancient chronicle. During a trip to Shanghai, she uncovers her birth mother's dark history-imprisonment and debts owed to the wrong people. Upon her return, Lu is terminated from her job and faces a corporate espionage lawsuit after her invention is leaked. But the past and present soon collide.