Poirot visits his dentist for a regular check-up one day, and was surprised to hear from his friend Chief Inspector Japp that the dentist, Henry Morley, had committed suicide some time after Poirot's departure. The man was not entangled in any form of financial or relationship troubles, nor did he seem particularly depressed on the day of his death. The only possible alternative of Morley's death is murder, but who could have killed him, and why? Among Morley's patients is Alistair Blunt, a major political figure whom many would love to see gone. Perhaps he's the intended target?
In 1992 it was adapted to TV for the 4th season of Poirot. Tropes unique to this adaptation are listed on the series page.
This novel provides examples of:
- Accidental Misnaming: Morley's bellboy, Alfred, always gets his customers' names wrong. For example, a certain Colonel Abercombie becomes "Arrow-bumby", while Poirot he calls "Peerer".
- Affably Evil: The killer is genuinely pleasant, and remained polite after Poirot reveals their schemes. They attempted to offer a deal to Poirot so that they could be set free, and when Poirot refuses, they gracefully (albeit regretfully) resigned to arrest.
- All Girls Want Bad Boys: Frank Carter is an obnoxious, good-for-nothing bully, but his lover Gladys is devoted to him, believing that her love would influence him for the better.
- Blackmail: Amberiotis is a known blackmailer and tries to blackmail Blunt for his bigamy. Unsurprisingly, he gets killed for it.
- Chekhov's Gun: As Poirot was leaving his dentist, he took a particular notice of a lady's buckled shoes. This plays a significant part in deducing who the murderer is.
- Feet-First Introduction: When Poirot encounters Miss Salisbury Seale for the first time, the latter was just coming out of the taxi, sticking out her buckled shoe. In fact, Poirot's first impression of her was what a well-shaped foot she had, though he was not much impressed by the rest of her.
- Graceful Loser: The killer didn't get angry, or try to make excuses, or attempt to harm Poirot when the latter confronts them with the truth of the murder. When Poirot refuses to withdraw from the case, they calmly respond:"Then I'm in for it. It's in your hands, Poirot. It's up to you.
- He Knows Too Much: Mr Blunt killed Amberiotis and Ms Salisbury Seale because the latter knew Blunt's first (and secret) wife, whom he did not divorce before his famous marriage to the wealthy Rebecca Arnholt and told Amberiotis about the fact, which he then used as blackmail material.
- Frank Carter is rude, obnoxious bully who can't hold down a job and borrows money from his lover. When he was framed for the murder of Morley and the attempted murder of Alistair Blunt, Poirot was quite tempted to not clear his name and let him hang.
- Howard Raikes was similarly unpleasant and extremely fanatical about his leftist ideals.
- Kill and Replace: Mabelle Sainsbury Seale was murdered, and (one of) the killers took her identity after her death. Likewise, Alistair Blunt murders Morley and pretends to be the dentist in order to kill the next patient, Amberiotis.
- The Needs of the Many: The killer's justification for committing the murders. He is the last remaining conservative among the political circle, whom many are trying to bring down. If he falls, he asserts, the nation would go down with him. He killed Amberiotis and Ms Seale because they knew about a scandal that would surely destroy his work. Morley's death is just a means to achieve the other two murders.
- No Hero to His Valet: Like most, normal mortals, Poirot is deathly afraid of the dentist, and is fully aware of the indignity of going through the dental procedures. He lampshades this in his monologue, saying that the idiom "no hero to his valet" would be more suitable when applied to one's dentist.
- Sadistic Choice: At the end of the investigation, Poirot is faced with two unpleasant choices: to reveal the truth and arrest the otherwise pleasant and unassuming character who stands for Poirot's own ideals, and who also happens to be the last Conservative champion whose removal from power could lead to economical instability and unrest on a national level, or keep silent and let the scapegoat — a crass, unpleasant individual whom Poirot considers a waste of space that the country could do without, but is otherwise innocent of the crimes pinned on him — take the blame and be hanged for it.
- Two Aliases, One Character: Mabelle Sainsbury Seale is actually Mrs. Albert Chapman, who herself is really Alistair Blunt's first wife, Gerda, who's been posing as his cousin! This is convoluted even by Christie standards.