John Dickson Carr (1906-1977) was an American MysteryFiction writer, frequently known as the master of the LockedRoomMystery. Several of his works were published under the pen-name Carter Dickson. (He also had a couple of other pen-names that he used very rarely.)

His best-known work is probably ''The Hollow Man'' (US title: ''The Three Coffins''), part of his on-going ''Dr. Gideon Fell'' series. (Fell himself was loosely modeled on writer Creator/GKChesterton). He also had a popular series starring the detective Sir Henry Merrivale, written as Carter Dickson. These two series make up a large portion of his work, but he also had a couple of other, smaller, series, and a number of standalone novels and stories.

He was a friend of Creator/ArthurConanDoyle (creator of ''Literature/SherlockHolmes''), and published a biography of Doyle in 1950. He also collaborated with Doyle's son on several Holmes stories after Doyle died.
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!! Tropes in his works:
* AbnormalAmmo: ''The Plague Court Murders'' involved a murder where the victim was [[spoiler:shot by a bullet carved from rock salt that dissolved in his body, leaving no trace]].
* AmateurSleuth: His portly master detective Dr. Gideon Fell, and Sir Henry Merrivale, the masters of the locked room murder.
* AndYouThoughtItWasAGame: In ''The Arabian Nights Murder'', a set of friends putting on an act to trick one of their buddies hires an actor to play a professor in an Arabian museum. They are surprised when a ''real'' professor, a friend of the museum's owner, arrives for a meeting and is treated as an actor who looks just like the real thing. In the meantime, the professor thinks that the actors are real, and attacks one of them in an act of misguided heroics.
* BangBangBANG: Averted in one novel, where a firecracker is used to fake the sound of a gunshot to throw off the investigation.
* BatterUp: The killer in [[spoiler: ''The Skeleton in the Clock'']] used a cricket bat.
* BeneathSuspicion:
** The killer in ''Below Suspicion'' was [[spoiler:in a prison cell when the murder was committed]].
** Remarked on in an essay on the FairPlayWhodunnit: "never remind the reader that a suspect has an airtight alibi, or he'll immediately be suspected. Treat it as such a given that it never occurs to the detective (or the writer!) to suspect Joe because Joe is so ''obviously'' innocent."
* BreakingTheFourthWall: In the classic LockedRoomMystery ''The Hollow Man'', one chapter consists of Dr Gideon Fell giving a lecture on Locked Room Mysteries in fiction. When asked what relevance this has to the situation, he replies "Because we're in a detective story, and we don't fool the reader by pretending we're not."
* BrotherSisterIncest: In ''The Demoniacs'', the early-eighteenth-century detective has come to suspect that his girlfriend is his half-sister. [[spoiler: She isn't.]] If she is, he wants to find and destroy the evidence so he'll be able to marry her anyway. When he admits that to her, [[spoiler: ''after'' finding out she isn't related]], she's pleased rather than squicked; she plainly feels it's ''romantic''.
* BuriedAlive: Part of the backstory of ''The Hollow Man''/''The Three Coffins'' was a jailbreak by live burial. There was a plague epidemic going on in that prison, and the escaper counted on the burial detail being in too big a hurry for little details like nailing the coffin lid tightly or shoveling very much dirt on top.
* TheCaseOf: Carr uses this template for ''The Case of the Constant Suicides'', one of the Gideon Fell mysteries.
* ConvictionByContradiction: Carr specifically warns aspiring mystery writers about this kind of clue in his essay "The Greatest Game in the World." Of course, if you do what he advocates, having guilt depend on a series of clues rather than just one, you won't have that problem.
* DeadPersonImpersonation: A major plot twist in his book [[spoiler: ''The Three Coffins/The Hollow Man'']] involves this.
* DeceasedFallGuyGambit: A variant occurs in ''[[spoiler:The Mad Hatter Mystery]]''; the killer tries to frame [[spoiler:the mad hatter]], knowing that [[spoiler:the dead man is the mad hatter]].
* DidYouDie: Invoked by Pierre Fley in ''The Hollow Man'':
* DyingClue: In [[spoiler: ''Patrick Butler for the Defense'']], the victim says before dying to the person trying to assist him "It was your gloves". [[spoiler:It had previously been established that the victim only spoke French and that a TranslationConvention was being used. In French, "your gloves" is "vos gants", which sounds similar to the murderer's name "Vaughan".]]
* {{Expy}}: "The Empty Flat" is a short story which opens with academic rivals Douglas Chase and Kathleen Mills meeting for the first time, not realising who the other is. A couple of years later, "The Case of the Constant Suicides" gives Alan Campbell and Kathryn Campbell similar personalities and the same MeetCute, and (being a full-length book) allows their relationship to be developed in more detail.
* FairPlayWhodunnit: His stories always showed you all the clues. The only problem was usually that the murder was ''impossible'' to begin with, so you couldn't figure out ''how'', much less who. Carr even [[LampshadeHanging lampshaded the tar out of this]] in ''The Three Coffins'' when Dr. Fell stops in the middle of the novel to explain all the ways you can do a locked room mystery, [[BreakingTheFourthWall because there was no point in pretending they weren't in such a novel]]. At the end of the chapter (yes, it's a full chapter of all the ways to pull one off) the other characters tell him that the two murders don't fit into ''any'' of his categories. [[spoiler: They're really wrong.]]
* FalseReassurance: Done in ''The Nine Wrong Answers'' in the form of footnotes that can be misleading at best, and a razor thin edge from outright lies at worst.
* FrightDeathtrap: His [[LockedRoomMystery locked room mysteries]], which might be called "howdunnits", included a couple like this, where the mystery was largely just how the victims had been scared to their deaths.
** In ''The Case of the Constant Suicides'', everyone who stayed in a certain room in a castle for a night would wind up falling down to their deaths from the dangerous balcony, as if something scared them into attempting to escape. There was nothing special in the room aside from a box with a cage door such as might be used to carry a small animal that had been brought in recently and left under the bed -- but which people had looked into and found it to be empty. [[spoiler: Actually it wasn't empty, but contained something nearly invisible -- carbon dioxide ice, which would start to vaporize as the temperature got lower at night, leaving the occupant of the room unable to breath and cause them to panic for some air.]]
** In ''He Who Whispers'', just after it has been suggested that one of the characters is a vampire and was able to commit a previous impossible murder by flying, a shot is heard, and one character is found in her bed scared so badly she has nearly died (and is incapable of explaining what has happened, of course). She's holding a gun and appears to have shot at something ouside the window, which is, of course, so far above the ground and inaccessible that only something flying could have been behind it. [[spoiler: The would-be-murderer -- who would have succeeded if he had had the right, much more sensitive target instead of the wrong person in the dark -- had in fact been in the room with the victim, pressed a gun to her head in the dark, and whispered to her a long time about how he was going to shoot her -- then fired the other gun he had towards the window, expecting her to die of shock when she thought she was being shot, but with it looking like she fired the gun herself.]]
* GenreSavvy: Dr. Gideon Fell is well aware that he's in a detective novel.
* HangingJudge: Justice Ireton in ''Seat of the Scornful'' / ''Death Turns the Tables'' is a HangingJudge who becomes the prime suspect.
* HiddenInPlainSight: In one story, a killer hides a glass knife by dropping it into a jug of water.
* HisNameIs: ''Dark of the Moon'' has one suspect go through this. Subverted in that she survives (though obviously she doesn't recover enough to say anything until after the killer's already caught) and [[spoiler:the fact that she was about to accuse someone of multiple crimes - including incest - that the accused ''didn't do''.]]
* IWasQuiteALooker: In ''The Demoniacs'', the hero's girlfriend discovers that a certain very decrepit old-looking woman is younger than she looks -- and might be her long-lost mother. The girl is quite upset by the possibility that she might come to resemble this hag.
* TheKillerWasLeftHanded: ''Death Watch'': An early clue establishes the killer was left handed. [[LampshadeHanging Lampshaded]] / [[SubvertedTrope Subverted]]: [[spoiler: It was part of a frame up by the real killer, and the detective has a brief rant about left-handed / right-handed clues.]]
* LockedRoomMystery: Carr, the acknowledged master of this back in the golden age of crime fiction, provided all sorts of different ways to accomplish this. In his book ''The Hollow Man''/''The Three Coffins'', series lead Dr. Gideon Fell actually gives a lecture on the different ways a locked room mystery can be created. If the detective is Fell, Henry Merrivale, or Henri Benicolin, there is an excellent chance you've got a locked room or impossible crime on your hands.
* MetaphoricallyTrue: ''The Nine Wrong Answers'' has authorial footnotes that use this trope to an almost gleeful extent, to the point that the final one points out that at no time did previous footnotes ''technically'' lie about niceties like [[spoiler:whether a man who was poisoned actually died, and whether a man really was who he was claiming he was.]] (Although some critics maintain that Carr slipped in a few places and really ''did'' make the "incorrect" claims.)
* NeedleInAStackOfNeedles: ''The Punch and Judy Murders'' has a [[spoiler: counterfeiter who hid the real money with the fake money]].
* NeverGetsDrunk: Dr Gideon Fell can put away enough booze to land any two normal men in the ER with alcohol poisoning without showing any sign. Probably because of pure body mass (if there's an Obese Detective trope, he's one of the poster children).
* NeverHeardThatOneBefore: The police surgeon in ''The Mad Hatter Mystery'' is called Doctor Watson, and complains that he's been the butt of Literature/SherlockHolmes jokes for thirty years.
* ObfuscatingDisability: The killer in [[spoiler: ''The Problem of the Wire Cage'' uses his recent car accident, and its attendant injuries,]] to pull off a murder he seemingly couldn't have physically committed. Unfortunately, circumstances turn it into a murder NO ONE could've committed.
* PutOnABus: Hard-drinking amateur detective Gideon Fell is married to a rabid teetotaler. Once the first novel was finished, Carr didn't so much put Mrs. Fell on a bus as he renovated the bus into a nice [=RV=] for her and sent her off for most of the series.
* RightHandCat: Etienne Galant, the BigBad in ''The Corpse in the Waxworks'', is seen stroking a white persian. The book was published in 1932.
* SinisterMinister: The 'helpful' clergyman of ''Hag's Nook''.
* SleepCute: In ''The Case of the Constant Suicides'', the first time Alan and Kathryn meet, the chapter ends with them sitting up at night arguing an academic point. The next chapter opens the following morning, with them waking from a SleepCute.
* TimeDelayedDeath: Used (in combination with a few other things that complicate it) in the classic LockedRoomMystery ''The Hollow Man''.
* TomatoSurprise: ''Below Suspicion'' has an opening scene from the point of view of a young woman accused of murder. In the narration, the woman desperately thinks to herself that she's not guilty of the crime, and is despairing of anyone believing her. Since this is an internal narrative, the reader can be assured that she is perfectly innocent, and she is. [[spoiler:Of the murder she's accused of. She is, in fact, guilty of another murder, and part of her despair is that her perfect alibi for the one she committed has left her open to the accusation of the one she didn't. Gideon Fell, the detective of the story, even lampshades this trope by noting that if anyone had been able to "read the thoughts" of the young woman, they would've seen a completely sincere and truthful plea for her innocence of the murder she didn't commit.]]
* TrailersAlwaysSpoil: The cover of the HarperCollins printing of ''The Case of the Constant Suicides'' features a dog carrier with strange fumes rising out of it. [[spoiler: This essentially gives away the murder method used in the book - a block of dry ice hidden in a dog carrier that releases carbon dioxide gas as it sublimates.]]
* TroubleEntendre: Occurs in a key scene in ''The Hollow Man''.
* WriteWhoYouKnow: Carr knew Creator/GKChesterton, the model for Dr. Gideon Fell, from the Detection Club.
* YouNeedToGetLaid: In a bit of UnfortunateImplications in ''The Hollow Man'', Dr Gideon Fell recalls a time he was chairing a debate on women's rights:
-->"... You were on the side for Women's Rights, Miss Grimaud, and against the Tyranny of Man. Yes, yes. You entered very pale and serious and solemn, and stayed like that until your own side began to present their case. They went on something awful, but [[DontShootTheMessage you didn't look pleased]]. Then [[StrawFeminist one lean female]] carried on for twenty minutes about what woman needed for an ideal state of existence, but you only seemed to get madder and madder. So when your turn came, all you did was rise to proclaim in silvery ringing tones that what woman needed for an ideal existence was less talking and more copulation. Or perhaps you didn't say copulation."

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