From a village made of hot-air balloons to a subterranean battle arena, two young people struggle to discover who and what they are — and how to use the astonishing powers they share.

High over China, twelve-year-old Mei arrives at the Sky Village, an intricate web of hot-air balloons floating above an Earth where animals battle machines for control. Deep below the ruins of Las Vegas, thirteen-year-old Rom enters a shadowy world where he is commandeered to fight, gladiator-style, against hybrid demons for the entertainment of a mercenary crowd. Mei and Rom have never met, but they share a common journal — a book that allows them to communicate with each other and reveals that they carry the strange and frightening Kaimira gene, entwining aspects of human, beast, and machine within their very DNA. In this thrilling, intricately plotted novel, Mei and Rom must find the courage to balance the powers that lurk within — and overcome outside forces that seek to destroy them — if they are to survive and save the ones they love.