Episodes run for either approximately 50 minutes or 90–100 minutes, the latter of which is the format of all episodes from series 6 onwards. The shorter episodes are based on Christie's short stories featuring Poirot, many published in the 1920s, and are considerably embellished from their original form. The longer episodes are based on Christie's 33 Poirot novels and one short story collection (The Labours of Hercules). While Christie's novels are set contemporaneously with the time of writing (between the 1920s and 1960s), 1936 was chosen as the year in which to place the majority of Poirot episodes; references to events such as the Jarrow March were included to strengthen this chronology. With some exceptions, the series as a whole is set in roughly chronological order between 1935 and 1939, just prior to the Second World War.[fn 1]
The Capture of Cerberus (written c.1939, posthumously published)
Not drawn on in any episode and unrelated to the better known final case of the same title in The Labours of Hercules.
Originally written to be the last of The Labours of Hercules, this story finds Poirot holidaying in Geneva, trying to take his mind off the impending war. But a chance meeting with an old acquaintance leads to an investigation involving a Nazi dictator and an enormous hound. Christie re-wrote the entire story due to its political content, retaining only the title.
Hercule Poirot and the Greenshore Folly (written 1954, posthumously published)
In 2012, Suchet performed a rehearsed reading of Black Coffee, produced and presented by The Agatha Christie Theatre Company, in aid of Chichester Festival Theatre's restoration fund. But the novel or play had not any adaptation in this TV series.
^Numerous references in early episodes place the series primarily in 1935, progressing to 1936 by series four. Most references remain to 1936, moving slowly forward to 1937 by series eleven and 1938 by Murder on the Orient Express. The Big Four is set explicitly in early 1939. The most notable exceptions to this chronology are The Mysterious Affair at Styles, which narrates Poirot's first case in 1917, and Curtain: Poirot's Last Case, which is set primarily in 1949. The Chocolate Box shows Poirot in the early 1900s, though the framing narrative remains consistent with the series' usual timeframe.
^Peril at End House was first broadcast as a two-part episode, both parts of which aired back-to-back. Subsequent showings and DVD releases present it as a single feature-length episode.
^DVD releases invert the order of series eight, placing Evil Under the Sun after Murder in Mesopotamia, and mislabeling the former episode's airdate as "15 December 2002" (which was the airdate for France), and the latter's airdate as "8 July 2001" (which was the U.S. airdate that aired first along with France's).
^Although the first UK broadcast was on 25 December 2009, Appointment with Death was already legitimately available to UK viewers, having been released on DVD with the rest of series eleven on 6 October 2008.
^The Clocks was intended to be placed before Hallowe'en Party, but in the UK ITV did not initially schedule its broadcast in favour of the latter episode and Murder on the Orient Express. All DVD releases restore the intended episode order.
^The Clocks was released on DVD, along with the rest of series twelve, in January 2011.
^Murder on the Orient Express was intended as the first episode of series twelve, but was held back until Christmas 2010 as a consequence of Appointment with Death's broadcast the previous year. All DVD releases restore the intended episode order.