"Murder in Black Letter" is a mystery novel written by Poul Anderson. The story likely centers around a murder investigation, as implied by the title. The use of "Black Letter" in the title may suggest a legal or historical context, as "Black Letter" can refer to a type of Gothic script used in legal and historical documents. This novel represents a departure from Poul Anderson's more typical science fiction works and delves into the mystery genre. However, without specific details about the plot and characters, it's challenging to provide a detailed summary of the book's content.