"Demon Thief" by Darren Shan follows the story of a young boy who discovers he possesses a unique ability that allows him to interact with the supernatural. As he grapples with his identity and the powers within him, he learns to navigate a world filled with demons and dark forces. The narrative blends horror with fantasy, illustrating the protagonist's journey of self-discovery and the consequences of wielding such power.

The quote "I know who the demon thief is - it's me!" encapsulates the protagonist's realization of his own darker inclinations. This moment reflects the internal conflict he faces as he confronts the implications of his actions and abilities. The story delves into themes of morality and the struggle between good and evil, as he learns that to embrace his identity may come with a heavy price.