Adaptational Nice Guy: In the story, Dr Bernard is rather cold and aloof towards Poirot, and did not treat Mr Maltravers when he was alive. In the adaptation Dr Bernard is amiable towards Poirot and helps him out during the investigation, and performed surgery on Mr Maltravers to help fix a bad ulcer.
Poirot and Hastings travel to Marsdon Leigh due to what appears to be a case that needs the great detective's little grey cells... then learn that they were summoned because the innkeeper wants their help to write his mystery story.
Poirot encourages Hastings and Japp to tour the village's wax museum, where they begin praising a sculpture that we're supposed to think is the sculpture of Poirot on display. He's greatly disappointed to see they're lavishing attention on a sculpture of Charlie Chaplin.
Busman's Holiday: Played with. Poirot goes to Marsdon Leigh because he's been called on to help solve a murder, when in reality his innkeeper wants his help to write said innkeeper's mystery story. Then just as Poirot and Hastings head back to London, they learn a local dies of mysterious circumstances, which forces Poirot to extend his stay.
Fanboy: Mr. Naughton the innkeeper is a big fan of Poirot, to the point where he invites the detective to his town to help him write his mystery novel under the guise of requesting help on a case. In the denouement of said episode, he declares that he'll be able to tell his children that he helped solve one of Poirot's cases after doing such.
I See Dead People: Mrs Maltravers claims to see the spirits of the dead around Marsdon Manor. It's later revealed to be an act, one she tried to use to frighten her husband to death, and is used to help reveal her as the culprit.
Moustache de Plume: Inverted. Samuel Naughton writes mystery novels under the name Clarissa Naughton, since apparently mysteries written by female writers sell better.
Named In The Adaptation: The Maltraverses are given the first names Jonathan and Susan. Captain Black is given the first name Andrew.
Poor Communication Kills: Somehow, Poirot failed to notice the part of Naughton's message that stated he wanted assistance for a book he was writing, which was why Poirot labored under the assumption that it was a real case.
Promoted to Love Interest: Downplayed. Captain Black is portrayed as attracted to Mrs Maltravers whereas there was no sign of this in the original story.
Wounded Gazelle Gambit: Mrs Maltravers puts chloroform into her own gas mask during a civil defense exercise in order to draw attention away from herself as a suspect.
Writer's Block: Mr Naughton asked Poirot for help in solving his mystery novel because even he was stumped at how to conclude it. Poirot points out after reading it that it's because every one of Naughton's suspects had a plausible alibi.
