Members of the Detection Club write chapters of a classic Golden Age style mystery, complete with maps of the scene. The twist is that each author writes a chapter using the detective and style of another author. Dorothy Sayers, for example used Anthony Berkeley's Roger Shearingham while Berkeley borrowed Lord Peter. Would probably have been more amusing if I had been familiar with all the fictional detectives. As it is, only Lord Peter and Gladys Mitchell''s Mrs. Bradley are known to me.