From the moment Carrie Cairncross enters Port Vernon's strange August fog, she wonders whether curious events are merely coincidences or indications of a deeper mystery. When Carrie and her friends Booj and Greg discover a magical shadow that takes them wherever they wish to be, they anticipate a week full of adventurous fun. However, they are totally unprepared to find themselves in the middle of a plot to steal the earth's animals, unpredictable journeys to past and future worlds, time and space warps emanating from their town, a ruthless search for eternal youth, and sinister forces that threaten to destroy the fabric of time. Help has been sent from the distant future in the form of a powerful horned man who can alter time as well as his appearance. Only Direk's incapacitating sensitivity prevents him from setting foot outside to resolve the increasingly bizarre situation. When Carrie brings Booj, Greg, Direk and herself face to face with the mystery's terrible source, she learns whether her newly found courage is real or only another fleeting effect of the time and space warps. And she realizes that her own actions can make a world-or two worlds-of difference.