Miss Marple is holidaying at the titular hotel, where she meets her old friend Lady Selina Hazy, and encounters a variety of other guests including the adventuress Bess Sedgwick, the young heiress Elvira Blake, her guardian Colonel Lunscombe, and the forgetful Canon Pennyfather. The latter is supposed to fly to Switzerland for a conference but misses his flight by a day, returns to the hotel, and is knocked unconscious, before waking up four days later outside of London near to a recent train robbery where witnesses say they saw him; Miss Marple also saw him leaving his room fully conscious several hours after he was knocked out. Meanwhile, Elvira's money is being held in trust until she comes of age, and she asks her guardians who would inherit if she died, and hints that she is planning to get married. Lady Sedgwick has concealed the fact that she is Elvira's mother, considering herself unsuitable, and both women are lovers of the racing-car driver Ladislaus Malinowski, whose car resembles one seen at the train robbery. Miss Marple has seen him with Elvira at a restaurant, and has also overheard Sedgwick talking to the hotel commissionaire, Michael "Micky" Gorman, with whom she was once secretly married in Ireland. When Elvira returns to the hotel on a foggy night, she is shot at by an unknown sniper; Gorman runs in front of her to shield her, and is himself fatally shot. Police Chief Inspector Fred "Father" Davy, already involved in the mystery, teams up with Miss Marple to uncover the various crimes
The novel has been adapted twice for the screen: firstly as a 1987 BBC film starring Joan Hickson, and secondly as a 2007 episode of ITV's Marple. The latter made many large changes to the plot, and its associated tropes can be found on the page for the TV series.
The story contains examples of the following tropes:
- Action Girl: Lady Sedgwick is an adventuress, and her action skills shine in the climax of the novel.
- Adaptational Karma: In the original novel, the murderer is not seen to be apprehended, although Chief Inspector Fred "Father" Davy vows to go after her. The Joan Hickson adaptation follows the killer's final line of the novel with Miss Marple's discovery of an incriminating diary, resulting in an arrest.
- After Action, Villain Analysis: Subverted. After Bess Sedgwick crashes and dies, her confession and motivations are discussed, when Miss Marple quietly reveals that she falsely confessed to protect her daughter Elvira, the real murderer.
- All for Nothing: It turns out that Elvira's fears about her mother's marriage to Gorman depriving her of her inheritance by making her "illigitimate" were unfounded, and thus, unknown to her, there was nothing for her to gain from killing him.
- Badass Driver: Lady Sedgwick turns out to be one. She commits suicide by crashing her car after driving very fast and recklessly, but Father notes that her driving was actually magnificent, and that against the odds she avoided any other casualties or property damage.
- Bad Habits: Canon Pennyfather is incapacitated and impersonated as part of a robbery, for which he is to be the scapegoat.
- Busman's Holiday: Jane Marple is roped into solving a murder while holidaying at the titular hotel.
- Climbing Climax: Near the end of the story, Lady Sedgwick confesses to the murder and then flees by climbing the drainpipe to the roof of the building, managing to elude all of Father's men, before scaling down the far side, driving away recklessly in her car and crashing fatally. She did this deliberately and the confession was a false one to protect her daughter.
- Comic-Book Time: After having been originally presented as a subversion of the "Victorian Aunt" stereotype in her initial appearences, Miss Marple is described as having had a "Victorian Aunt" of her own in this novel of 1965.
- "Could Have Avoided This!" Plot: If Elvira Blake had just talked to a probate lawyer about her father's will, she would have found out the murder was completely unnecessary.
- Face of an Angel, Mind of a Demon: Miss Marple references this trope in regard to the murderer:"The children of Lucifer are often beautiful - and, as we know, they flourish like the green bay tree."
- False Confession: Bess Sedgwick makes one in order to protect the real killer, who is her daughter.
- Heroic Sacrifice: Bess Sedgwick pulls one in order to cover for Elvira.
- Love Makes You Evil: Elvira Blake was desperately in love with Malinowski, but knew that he would only marry her for her money. She killed Gorman out of fear that because his marriage to her mother made her father's marriage bigamous, Elvira might have, due to being "illigitimate", lost her inheritance, and thus also lost Malinowski. As it turned out, this fear was baseless.
- Murder by Mistake: Micky Gorman is accidentally shot while defending the intended victim from an unknown assailant. Or so it seems; the so-called "intended victim", Elvira, was the actual assailant who deliberately killed Gorman.
- Oops! I Forgot I Was Married: Lady Sedgwick and Micky Gorman had married in Ireland, and he had told her that it was just a game and not a legal union, but in fact the marriage was genuine, making all four of her subsequent marriages unwittingly bigamous.
- Scatterbrained Senior: The elderly and forgetful cleric Canon Pennyfather, who arrives one day late to the airport for his flight.
- Sibling Triangle: Actually a parent-child triangle, as both Lady Sedgwick and her daughter Elvira have been lovers of racing-car driver Ladislaus Malinowski.
- Unbuilt Trope: Adaptations of Agatha Christie works since the 1970s have sometimes been criticised for romanticising and idealising the Genteel Interbellum Setting. One of the last Miss Marple novels, At Bertram's Hotel, written and set in the 1960s, depicts the "timeless" and old-world atmosphere of the titular London hotel as a front for a criminal conspiracy, and ends with Miss Marple deciding that one must accept that the world has changed and not try to live in the past.
- The Unfettered: Lady Sedgwick, the adventuress. Discussed by Police Chief Inspector "Father" Davy.Father: "She's a woman in a thousand, you know. One of the wild ones. Oh, we've some of them in every generation. You can't tame them, you can't bring them into the community and make them live in law and order. They go their own way... They'd have been all right, I suppose, born in another age when it was everyone's hand for himself, everyone fighting to keep life in their veins. Hazards at every turn, danger all round them, and they themselves perforce dangerous to others. That world would have suited them; they'd have been at home in it. This one doesn't."