"The Angel of Darkness" is a historical mystery novel written by Caleb Carr, published in 1997. It is a sequel to Carr's earlier work, The Alienist, and continues the story of Dr. Laszlo Kreizler, a criminal psychologist in New York City during the late 19th century. The plot revolves around a series of gruesome murders and the investigation into the disappearance of a young girl. The novel explores themes of psychology, crime, and the societal issues of the time, including the treatment of women and the challenges faced by law enforcement. As Kreizler and his team delve deeper into the case, they confront the dark underbelly of New York and the complexities of the human mind.