"The Shadow Thief" is a novel by Annette Curtis Klause that follows the story of a young boy named Zachary who discovers he has the ability to steal shadows. This unique power leads him on an adventure filled with mystery and danger as he learns about the consequences of his actions. As Zachary navigates his new abilities, he encounters various characters, including a girl named Lily who becomes his ally. Together, they face challenges that test their friendship and courage, ultimately leading to a deeper understanding of themselves and the world around them.