The Judas window: a Sir Henry Merrivale mystery

Only young James Answell could have committed the murder. After all, he was found unconscious in the locked room next to the body of the murdered man. His clothes were disheveled from an apparent struggle. The whiskey decanter containing the liquor he said was used to knock him out was full to the brim. All the glasses on the table were clean. His fingerprints were found on the murder weapon, an arrow from the victim's collection. Furthermore, he was heard arguing with the dead man, whose daughter he wished to marry. Just about everyone is convinced that James is headed for a date with the hangman. Everyone except Sir Henry Merrivale, H.M. to his friends and associates. He's convinced that the real murderer used a Judas window" to commit the crime. Pay no attention to the architects who designed the building, H.M. insists. In fact, he says, you'll find a Judas window in practically every room. The trouble is that so few people ever notice it." First published in 1938, The Judas Window is considered by many to be the best locked room mystery of all time. Carter Dickson is, of course, the pseudonym of John Dickson Carr, the universally acknowledged grand master of the form.