At the programme's conclusion, which finished with "Curtain: Poirot's Last Case", based on the 1975 novel of the same name,[2] every major literary work by Christie that featured the title character had been adapted.

Several actors played multiple parts specific to certain episodes, including Nicholas Farrell and Beatie Edney.

[4] While Christie's novels are set contemporaneously with the time of writing (between the 1920s and 1970s), 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.

The Chocolate Box shows Poirot in the early 1900s, though the framing narrative remains consistent with the series' usual timeframe.

Recurrent motifs in the additions included drug use, sex, abortion, homosexuality, and a tendency toward more visceral imagery.

The visual style of later episodes was correspondingly different: particularly, an overall darker tone; and austere modernist or Art Deco locations and decor, widely used earlier in the series, being largely dropped in favour of more lavish settings (epitomised by the re-imagining of Poirot's home as a larger, more lavish apartment).

[7] However, a more upbeat string arrangement of the theme music is used for the end credits of "Hallowe'en Party", "The Clocks" and "Dead Man's Folly".

In flashback scenes, later episodes also made extensive use of fisheye lens, distorted colours, and other visual effects.

Series 10 (2006) introduced Zoë Wanamaker as the eccentric crime novelist Ariadne Oliver and David Yelland as Poirot's dependable valet, George — a character that had been introduced in the early Poirot novels but was left out of the early adaptations to develop the character of Miss Lemon.

Comedian and novelist Mark Gatiss wrote three episodes and also guest-starred in the series,[12] as have Peter Flannery and Kevin Elyot.

[13] The final episode to be filmed was "Dead Man's Folly" in June 2013 on the Greenway Estate (which was Agatha Christie's home) broadcast on 30 October 2013.

[16] Suchet, a method actor, said that he prepared for the part by reading all the Poirot novels and every short story, and copying out every piece of description about the character.

[17][18][19] Suchet told The Strand Magazine: "What I did was, I had my file on one side of me and a pile of stories on the other side and day after day, week after week, I ploughed through most of Agatha Christie's novels about Hercule Poirot and wrote down characteristics until I had a file full of documentation of the character.

[22] According to many critics and enthusiasts, Suchet's characterisation is considered to be the most accurate interpretation of all the actors who have played Poirot, and the closest to the character in the books.

Alongside recurring characters, the early series featured actors who later achieved greater fame, including Sean Pertwee ("The King of Clubs", 1989; "Dead Man's Folly", 2013), Joely Richardson ("The Dream", 1989), Polly Walker ("Peril at End House", 1990), Samantha Bond ("The Adventure of the Cheap Flat", 1990), Christopher Eccleston ("One, Two, Buckle My Shoe", 1992), Hermione Norris ("Jewel Robbery at The Grand Metropolitan", 1993), Damian Lewis ("Hickory Dickory Dock", 1995), Jamie Bamber ("The Murder of Roger Ackroyd", 2000), Russell Tovey ("Evil Under the Sun", 2001), Kelly Reilly ("Sad Cypress", 2003), Emily Blunt ("Death on the Nile", 2004), Alice Eve ("The Mystery of the Blue Train", 2005), Michael Fassbender ("After the Funeral", 2006), Aidan Gillen ("Five Little Pigs", 2003), Toby Jones and Jessica Chastain ("Murder on the Orient Express", 2010), and Tom Ellis ("Dead Man's Folly", 2013).

Four Academy Award nominees have appeared in the series: Sarah Miles, Barbara Hershey, Elizabeth McGovern and Elliott Gould.

Peter Capaldi, Jessica Chastain, Michael Fassbender, Lesley Manville, Vanessa Kirby and Emily Blunt went on to receive Academy Award nominations after appearing on the show (with Chastain winning the Best Actress award in 2022 for The Eyes of Tammy Faye).

He meets Christie's grandson Mathew Prichard who recounts how his grandmother found the character amongst Belgian refugees in Torquay.

Suchet notes a conscious decision was made by the film company to portray Poirot without a moustache.

Suchet also goes to Florin Court, a place that the production company chose to represent his home Whitehaven Mansions.

Finally, Suchet travels on the Orient Express and recounts filming the episode "Dead Man's Folly" last at Greenway to finish on a high note.