The body of a young pretty girl, Ruby Keene, is found unexpectedly on the floor of the respectable old couple Mr. and Mrs. Bantry. They have no idea who she is and how she got there. Mrs. Bantry, remembering her old friend Miss Marple, who is known for her deductive abilities, calls the latter so the two of them can investigate this murder alongside the local police.
It is soon revealed the girl was a dancer at a nearby seaside hotel so Miss Marple decides to go there to talk with her colleagues and also with the elderly Mr. Jefferson, a dying millionaire who is revealed to have changed his will to include the victim as his beneficiary, in detriment to his son- and daughter-in-law. But the Bantrys' neighbour, Basil Blake, an allegedly dissolute young man involved in the movie industry, also sees himself suspected.
Adapted for TV in 1984 by the BBC and in 2004 by ITV.
This novel contains examples of:
- Affectionate Parody: The "body in the library" had become such a hoary old cliché of detective-fiction writing that Christie deliberately wrote The Body in the Library as the most outrageous send-up of the idea that she could manage whilst still making it a serious murder mystery.
- Bluffing the Murderer: Miss Marple forces the killer to reveal themselves by having Mr. Jefferson announce that he's going to donate the money he had intended to bequeath to Ruby away. The killer was apprehended when they attempted to murder the old man that very night.
- Celebrity Paradox: The young son of Adelaide Jefferson namedrops several of his favourite mystery writers including... Agatha Christie herself.
- The Ditz: One of the suspects, George Bartlett, is a very absent-minded and inarticulate fellow who can't seem to get to his point, and keeps on forgetting what he's been doing. The police gets exceedingly annoyed trying to get anything useful out of him.
- Dub Name Change: In-Universe. Raymond Starr's real name is "Ramon" (he's Argentinian), but he changes it to "Raymond" to make it sound more English.
- Eureka Moment: Basil Blake's girlfriend (actually wife) prompts Miss Marple to have one of these, by saying that all marriages are on record and can easily be verified. This is how she finds that Josie Turner and Mark Gaskell are married and that they are the murderers.
- Gold Digger: Played with; everyone pretty much accuses Ruby Keene of being one of these, but are (grudgingly) willing to point out that there was no malice in her, as a poor girl she could hardly be faulted for not turning down the possibility of coming into a large sum of money and that the other people surrounding Conway Jefferson, much as they might not have liked the situation, weren't exactly entitled to his money either.
- Hypocritical Humor: When Miss Marple briefly visits the vicar's wife Griselda, she finds her tending to her newborn son. Griselda informs her that she doesn't fuss or bother over or play with him much, because all the books she's read on parenting say that "a child should be left alone as much as possible" Naturally, as soon as Miss Marple has left, she is fussing and bothering over and playing with him as much as humanly possible.
- Inverted Trope: Although most of the books it parodies have been long-forgotten, the novel actually inverts a then-popular murder mystery trope/cliche regarding someone being murdered in the library of a big fancy house. Usually, the library would be revealed to have all kinds of unusual features (secret trapdoors, hidey-holes and passageways, hidden weapons and the like) which would be used to explain how the murder was committed. Christie inverted the trope by making the library itself utterly mundane and containing absolutely nothing which one would not otherwise expect to encounter in a library, but making the body itself unusual and out-of-place.
- Jerk with a Heart of Gold: Basil Blake presents himself as one of those loud, disrespectful and obnoxious jacknape who goes out of his way to annoy the "old geezers" in the village. He is also a good-hearted young man who risked his life to rescue a family (including their dog) from a burning building.
- Malicious Slander: When the dead body of an exotic young girl was found in the Bantrys's library, pretty much all of St. Mary Mead began whispering about how the old colonel must have had an affair with the murder victim, and probably killed her too. The only people who do not buy into this unpleasant gossip are Mrs. Bantry, Miss Marple herself and the vicar.
- Mama Bear: A lot of emphasis is put on how devoted of a mother Adelaide is towards her young son Peter, and her desire to secure more money for the boy makes a very strong case against it. In the TV series, this is one of the reasons why she was driven to murder.
- Model Scam: One of the victims was reported missing after going to meet a suspicious "film producer" who had offered her to audition for a filming test.
- Replacement Goldfish: Mr. Jefferson saw the victim as a replacement to his dead daughter, Rosamund, whom he was most fond of. After her death, he realises that, in hindsight, the qualities he saw in Ruby are really just his own projections of Rosamund.
- Shout-Out: Hugo McLean is compared to Dobbin of Vanity Fair.
- Slap-Slap-Kiss: When Melchett confronts Basil Blake about the dead body, Basil's girlfriend, Dinah, interrupts them, and the two lovebirds had a huge row in front of the colonel, forcing him to leave. Such public display was how Miss Marple deduced that the two are actually married.
- The Unfavorite: While they're not his biological children, Mr. Jefferson clearly favours Adelaide to Mark, and the only reason he put up with Mark at all is because he's the husband of his favourite child, Rosamund. Of course, this is justified because Adelaide is the one who takes care of the old man and accompanies him in his loneliness (until Ruby comes along, that is), while Mark is a selfish Jerkass.
- "Well Done, Son!" Guy: It is said that Frank Jefferson got into trading to prove himself as capable as his father, who is a successful businessman. When his investments go wrong, Frank does not dare to ask his father for financial help, for fear that the old man would be disappointed in him.
- Widow Woman: Adelaide Jefferson has been married twice, and both husbands died shortly after the marriage. The second husband, Frank, even drove them into bankruptcy after a series of bad investments. In the 2004 adaptation, it is implied that her disappointing marriages with men is what caused Adelaide to eventually be involved in a lesbian relationship with Josie.