The Hollow Man is a 1935 locked room mystery novel by the American writer John Dickson Carr, featuring his recurring investigator Gideon Fell. It contains in chapter 17 the often-reprinted "locked room lecture" in which Dr Fell speaks directly to the reader, setting out the various ways in which murder can be committed in an apparently locked room or otherwise impossible situation.
Not who you're looking for? Others named The Hollow Man: 2011 novel by Oliver Harris · 1992 novel by Dan Simmons