Adaptational Karma: Inverted. Murderess Mrs Lorrimer was killed in the novel, but in the adaptation she is allowed to live, and is never prosecuted for murdering her husband.
Superintendent Jim Wheeler, who is the series' version of Superintendent Battle, tries to retrieve scandalous photographs of him (and, it is implied, Shaitana) from a homoerotic photography studio.
Dr Roberts and the offscreen Mr Craddock are in a sexual relationship. Both men were heterosexual in the original novel, and it was Mrs Craddock with whom Dr Roberts had the relationship.
Shaitana is given an Ambiguously Gay flamboyance (although YMMV on whether that was present in the book or not) and has ties to the aforementioned photography studio, and possibly Superintendent Wheeler.
The originally heterosexual Rhoda Dawes is here implied to be a lesbian Yandere who possessively loves Anne Meredith.
Adaptational Villainy: The episode turns Rhoda Dawes from a good-natured adventurous woman into an implied lesbian who killed Anne Meredith's employer, Mrs. Benson, and attempts to do the same to Anne, rather than the other way around.
A woman who had just threatened her doctor to expose him for seducing her husband would definitely not want him putting his hands on her to give her an inoculation for overseas travel. Why didn't Mrs. Craddock go to a different doctor?
Poirot still brings up his failure "28 years prior", but since in the adaptation of "The Chocolate Box" he successfully figured out who the murderer was, it begs the question of what said failure really was.
Bury Your Gays: Rhoda Dawes is implied to be a lesbian who possessively loves her housemate, Anne Meredith. When the latter tries to leave to marry someone else, Rhoda attempts to kill Anne in a fit of jealous rage, but it backfires, and she dies instead.
But Not Too Gay: Dr Roberts's false account of his relationship with Mrs Craddock is accompanied by a racy "flashback", but nothing is shown when it's revealed that he's actually sleeping with her husband. In fact, despite being the reason for the doctor's initial murder, Mr Craddock never appers in the flesh at all.
Canon Foreigner: A posthumous example. Herbert Meredith was Mrs. Lorrimer's first husband and Anne Meredith's father, facilitating them being Related in the Adaptation.
Death by Adaptation: The episode switches the roles of Rhoda Dawes and Anne Meredith. Rhoda is therefore one who drowns, while the now innocent Anne survives to marry Major Despard.
Deliberate Values Dissonance: The murder was committed in part to cover up a gay love affair, which could have ruined the killer's career. When Poirot reveals this at the end, everyone in the room shifts around uncomfortably.
Detective Mole: Downplayed. One of the four "sleuths", Jim Wheeler (Superintendent Battle's adaptational replacement), finds himself becoming a suspect, but is ultimately found innocent.
Major Despard still shoots Mr Luxmore, but in this case it's because Luxmore was researching psychotropic drugs - he became violent and attacked his wife after imbibing one of his concoctions, and Despard shot him to save her life.
Mrs Lorrimer still kills her husband as in the original, but this time the husband she kills is her first husband, Herbert Meredith, and she kills him by pushing him down the stairs. For that matter, her second husband, Mr Lorrimer, dies of natural causes instead.
Does Not Like Men: Rhoda Dawes, in complete contrast to her counterpart from the original novel.
Novel!Rhoda:(sighing) [Despard's] got such a lovely back to his neck. Very brick red and muscular.
Adaptation!Rhoda:(angrily) Despard's a brute. That great thick neck. Honestly, Anne, how could you?
Have I Mentioned I Am Heterosexual Today?: Superintendent Wheeler makes an allusion to his "wife and kids" when he retires from the bridge game before discovering Mr. Shaitana's death. Given that Poirot discovers he's gay at the end of the episode, it's left unclear whether Mrs. Wheeler and the children actually do exist.
Necro Cam: Poirot's summation is accompanied by a flashback of how the crime was committed. However, unusually for this series, we also get several false "flashbacks" throughout the episode, each showing how each of the suspects could have done it.
Related in the Adaptation: Mrs. Lorrimer is revealed to be the mother of Anne Meredith in this version, in order to strengthen her motive for covering for her.
The episode switches the roles of Anne Meredith and Rhoda Dawes, and gives the respective characters an Adaptational Heroism and Adaptational Villainy by making Rhoda the true culprit of the murder Anne was suspected of. The innocent one ends up as the winner of their Love Triangle with Major Despard, while the murderer gets a Laser-Guided Karma and drowns while trying to do the exact same thing to their supposed "best friend".
In the original novel, Mrs Craddock was Dr Robert's lover and Mr Craddock was the angry spouse who was murdered by Dr Roberts after threatening to expose him. This adaptation swaps around Mr and Mrs Craddock's roles in this respect.
Series Continuity Error: Averted. The original story included a reference to Murder on the Orient Express. As this episode came before the adaptation of that story, the reference is changed to a similar but distinct crime Poirot investigated at some point.
Spared by the Adaptation: Mr. Craddock, Mrs. Lorrimer and Anne Meredith all died in the original novel but survive in this version.
Suicide by Cop: In this version of the story, Shaitana deliberately tempted four potential murderers to off him and then drugged himself; this did not occur in the novel.
Summation Gathering: The killer is revealed this way, in another departure from the book.
Suspiciously Similar Substitute: Colonel Hughes replaces Colonel Race, who previously appeared in Death on the Nile. Apparently, the actor was unavailable for this episode.
Yandere: Rhoda Dawes in this adaptation, whose possessiveness toward her friend and roommate Anne Meredith drives her to murder her aunt Mrs. Benson to prevent the latter from having Anne arrested and imprisoned for stealing, while strengthening her hold over Anne by allowing her to think herself guilty of the murder. When Anne finally expresses her determination to run away with Major Despard, Rhoda first threatens to inform on her for the aforementioned crime, and then attempts to drown her in the river. None of this occurs in the original novel.
