Classic Detective Fiction:

The Golden Age between the wars (1919 - 1939)

Development of formal rules for detective stories

• S.S. Van Dine: Twenty Rules for Writing Detective Stories (1928)
• Ronald A. Knox: Detective Story Decalogue (1929)
• Detection Club Oath: No Divine Revelation, Feminine Intuition, Mumbo-Jumbo, Jiggery-Pokery, Coincidence or Act of God (c.1928)
• Rules broken almost immediately: Christie, Iles, others

Closed societies

• The village ('Mayhem Parva')
• The university (Oxbridge)
• Murder in the manor (and locked rooms)
• Upper and upper-middle classes (the butler didn't do it)
• Clues, clues, clues -- and lots of red herrings

Aristocratic sleuths (and silly asses)

• Campion (with royal connections): Margery Allingham
• Wimsey (younger son of a duke): Dorothy L. Sayers
• Philo Vance (American aristo): S. S. Van Dine
• Henry Gamadge (old New York family): Elizabeth Daly
• Inspector Roderick Alleyn (brother of baronet): Ngaio Marsh

A quick detour: misogyny, racism, and just plain thuggery:

• Snobbery with Violence (Colin Watson; 1971)
• 'Sapper': Bulldog Drummond
• E. W. Hornung: Raffles
• Edgar Wallace: J. G. Reeder
• Schticks: 'yellow peril'; gentlemen-crooks; violence; all for England

Reaction against the pure puzzle

• The detective story as novel of manners: Dorothy L. Sayers
• Growth in characterization: Ngaio Marsh, Margery Allingham, Josephine Tey, Ellery Queen (later novels)
• 'Inverted' stories: R. Austin Freeman, Francis Iles (and Columbo)
• Psychological complexity: Michael Innes, Michael Gilbert, Nicholas Blake, Helen Eustis (The Horizontal Man; 1946)
• American Masters: Ellery Queen, Rex Stout, Elizabeth Daly, Phoebe Atwood Taylor
• Locked rooms and impossible crimes: John Dickson Carr, Clayton Rawson, Christie, Queen, Anthony Boucher
• HIBK ('Had-I-but-known'): Mary Roberts Rinehart, romantic suspense

Other Golden Age writers (and their heirs):

• Cyril Hare
• Philip MacDonald
• John Rhode
• Josephine Bell
• Edmund Crispin
• P.D. James
• Amanda Cross
• Jane Langton
• Emma Lathen
• Robert Barnard

Important points:

• Murder investigation as intellectual game with reader
• Importance of physical 'clews'
• Relatively bloodless: murder offstage
• Emotional effects of crime rarely seen
• Amateur investigators: the Jessica Fletcher syndrome
• Return to 'moral order' when crime solved - W. H. Auden, The Guilty Vicarage; 1948