Emma Sweeney has the potential to become an exceptional Watcher, but her instructors are losing patience with her. Raised by an Earth family, Emma is prone to emotional human behavior that gets the better of her logical Watcher instincts. Emma's Earth mother, Leto, is dying in the island world of Argadnel. Longing to be reunited with her human daughter, Ailla, who was stolen at birth, she has lost her will to live. Emma has pledged to find the missing child, but the quest becomes a dangerous race when Emma realizes she isn't the only one searching for Aila.