© ITV
I thought it might be useful to see a list of all the episode to date - with my chronology placement in brackets. I've chosen not to add the dates of the no-reference episodes. As you can see, most of the episodes actually fit well together. If you accept my chronology, series 1-2 mainly concentrate on 1934 and 1935, series 3-8 on 1935-36 and series 9-12 on 1936-38. It's also interesting to note the consistency in development of Poirot's life ("detective agency" with Miss Lemon and Capt. Hastings, "consulting detective" on his own, new/old apartment, active years/retirement etc.).
The first series of episodes (1989):
- The Adventure of the Clapham Cook (July 1935)
- Murder in the Mews (November 1935)
- The Adventure of Johnnie Waverly
- Four and Twenty Blackbirds (June 1934)
- The Third-floor Flat
- Triangle at Rhodes (October/November 1934)
- Problem at Sea
- The Incredible Theft (October 1936)
- The King of Clubs
- The Dream (probably early 1936)
The second series of episodes (1990):
- Peril at End House (probably summer 1935)
- The Veiled Lady (July 1935 or 1936 - placed in July 1935)
- The Lost Mine (February 1935)
- The Cornish Mystery
- The Disappearance of Mr. Davenheim
- Double Sin (October 1935)
- The Adventure of the Cheap Flat (November 1936)
- The Kidnapped Prime Minister
- The Adventure of the Western Star
- The Mysterious Affair at Styles (June 1917)
The third series of episodes (1991):
- How Does Your Garden Grow? (May 1935)
- The Million Dollar Bond Robbery (May 1936)
- The Affair at the Victory Ball (November 1935)
- Wasp's Nest (August 1934)
- The Tragedy at Marsdon Manor (September 1935)
- The Double Clue
- The Mystery of the Spanish Chest
- The Theft of the Royal Ruby (December 1935)
- The Plymouth Express
- The Mystery of Hunters Lodge
The fourth series of episodes (1992):
- The A.B.C. Murders (August/September 1936 - placed in August 1933)
- Death in the Clouds (June/July 1935)
- One, Two, Buckle My Shoe (August 1937)
The fifth series of episodes (1993):
- The Adventure of the Egyptian Tomb (June/January 1934/1936 - placed May 1934)
- The Under Dog (June 1936)
- Yellow Iris (September 1936)
- The Case of the Missing Will (June 1936)
- The Adventure of the Italian Nobleman (September 1935, possibly 1936)
- The Chocolate Box (early 1900s/mid-1930s)
- Dead Man's Mirror (March 1936)
- The Jewel Robbery at the Grand Metropolitan
The sixth series of episodes (1995-96):
- Hercule Poirot's Christmas (December 1936)
- Hickory Dickory Dock (April 1934 / October 1936 - placed in April 1936)
- Murder on the Links (July (May) 1936)
- Dumb Witness
The seventh series of episodes (2000):
- The Murder of Roger Ackroyd
- Lord Edgware Dies (June/July 1936 - placed in June/July 1937)
The eigth series of episodes (2001):
- Evil under the Sun (August 1936)
- Murder in Mesopotamia (January 1938)
The ninth series of episodes (2003-04):
- Five Little Pigs (June - placed in June 1937)
- Sad Cypress (September 1937)
- Death on the Nile (Jaunary 1936)
- The Hollow (September 1938)
The tenth series of episodes (2005-06):
- The Mystery of the Blue Train (May 1936 - placed in May 1937)
- Cards on the Table
- After the Funeral (July 1936)
- Taken at the Flood (possibly 1936 - placed in September/October 1937)
The eleventh series of episodes (2008):
- Mrs McGinty's Dead (October 1940 - placed in 1938)
- Cat Among the Pigeons
- Third Girl (1937 - placed in October)
- Appointment with Death (1937 - placed in January)
The twelfth series of episodes (2010-11):
- The Clocks (late 1930s)
- Three Act Tragedy
- Hallowe'en Party (October/November)
- Murder on the Orient Express (January/February 1938)
The thirteenth series of episodes (2013):
- Elephants Can Remember (1938)
- The Big Four (March/April 1939)
- Dead Man's Folly
- The Labours of Hercules
- Curtain (October 1949/February 1950)