But is it a Locked Room Mystery? The case of the impossible alibi.

Recently I was having a chat with a friend about impossible crimes (believe me this doesn’t happen that often), and though not a big reader they loved the series Death In Paradise. In response to my statement that I liked the impossible episodes of the series so far, they said “but aren’t all the episodes impossible crimes, because no one could have done it?”


In the intro to his brilliant CADS magazine number 74, editor Geoff Bradley writes a lovely off-hand piece about Death In Paradise, and its wave of bad press despite it’s popularity, (something I considered in this post). In his intro he also calls the stories of the BBC series ‘impossible crimes’.

Both these examples got me thinking. The idea that these stories are all being considered ‘impossible crimes’ seems to be because usually everyone has an alibi. This point of view doesn’t just apply to the TV series, but also to novels I have seen in discussion online. Some have suggested a novel as an impossible crime or locked room mystery because all the characters claim to be elsewhere at the time of the murder.

At the risk of treading some old ground covered by JJ somewhat in this post from last year, (it’s worth reading his post to see how he defines the terms ‘locked room’ and ‘impossible crime’ generally), I want to add my voice into the mix on this more specific point. I do not think a novel or episode of detective fiction counts as an impossible crime or locked room mystery simply if all the characters have seemingly solid alibis, and that is your complete set up. Why do I think this? Well, I think it’s something to do with the fact that an alibi and the impossible or locked room element of a novel are two very different things, with different roles.

Alibis are often created to be broken or solidified and therefore, even if seemingly watertight surely they can’t be the edges of an impossibility for the fact that most of the time they don’t hold up under scrutiny, or are meant to be broken down. Another problem is that the alibi can also be a lie. Many characters may say that they weren’t there or provide themselves with a place to have been, but that doesn’t mean it’s true. I think for a story to qualify as an impossible crime or locked room mystery something impossible has to have taken place, not just that there is a murder in an easily accessible location or within a generally plausible murder situation and everyone says ‘I wasn’t there.’

Seeing as Death In Paradise was the beginning of this thought process, let’s take the set ups of two episodes from series one as an example. Episode 1: ‘Death in Paradise’ tells the tale of a British detective shot while locked inside a solid steel panic room. Only the police know the code to the door, and when they get inside he has been shot at close range, no weapon and no murderer left within. The killer has somehow vanished into thin air. Therefore the physical circumstances under which the murder occurs are baffling and not able to have taken place, in other words an impossible crime. In Episode 3: ‘Predicting Murder’ (the series masterpiece I think) a woman is found poisoned in the classroom of a local school. There are two shot glasses on the teacher’s desk, and a bottle of strong drink, with only hers and the head teachers fingerprints, and only her glass poisoned. For the time of the murder however, the head teacher has an unbelievably rock solid alibi: “So let me get this straight, your alibi is that you were doing charity work, in an orphanage surrounded by nuns.” And so does everyone else who was involved in the school. This I would say, however, is not an impossible crime. The murder method and setup while complex, are not ‘impossible’ to occur, in that anyone could come and go into the room as they wished, even someone outside the cast of suspects could be responsible, and although they have alibis they were not all continuously watched, and it doesn’t mean that they are not lying or conspiring together. It seems as if complicated or tricky murder set-ups are being confused with an impossible or locked room set-ups.

‘Predicting Murder’

But maybe I am on shaky ground here? Alibis do often provide or hold together an impossibility. We could take the most classic locked room trope of the ‘first on the scene’ as an example. Used countless times over the years, here the alibi is: ‘We were all together when we broke down the door and the victim was found stabbed inside’, which is also the crux of the impossibility/solution ‘you were there, but when you went to examine the victim, who was only incapacitated, you stabbed them without anyone realising.’ Here then the alibi and the mechanics of the impossibility serve each other. Another example could be Keigo Higashino’s Salvation of a Saint (2008), we know who the murderer is, but we also know that she was on the other side of Japan at the time of the murder, so how on earth did she do it? Her alibi is, in essence, the impossibility.

Here I could run into even more problems, in that sometimes an impossible crime story is only such because a character’s testimony says so, but they are later found to be lying. Does that then mean the novel has changed from impossible to not? Or as was discussed a little in the comments on JJ’s post, Carter Dickson’s Judas Window (1938), one of the most important locked room mysteries ever written, requires us to believe that the central figure is innocent for the impossibility to even be there.

But in saying all this, I believe my point still stands, because I would say the impossibility in the ‘first on the scene’ scenario suggested above is: that they were stabbed in a room locked from the inside, but the killer managed to vanish away. Perhaps it’s the circumstances of the type of murder itself, rather than the alibis of those involved taking priority? Maybe it’s something to do with a mix up between the ‘howdunit’ and the ‘whodunnit’ and where final boundaries lie?

So what do you say? I would love to hear your thoughts on what you think constitutes a locked room proper, and how alibis play into that, as I try to traverse this rather narrow, icy path of definitions (leaving no footprints as I go).

22 thoughts on “But is it a Locked Room Mystery? The case of the impossible alibi.”

  1. Well, allow me to be the first to weight in: firstly with my thanks for your implication that my meanderings are in any way relevant to this discussion, and secondly with a Venn diagram of sorts…

    See the Alibi Problem and the Impossible Crime have a hefty overlap — there are at least two classic examples by Carr alone where the problem is only impossible because one character gives another a false alibi, or at least fails to contradict evidence by a third character where they have the knowledge to do so. I completely agree that the comission of the crime should have more to it in order to appear impossible rather than simply having everyone go “Er, I was elsewhere” (I’ve just finished Death on the Nile, which was posited as an impossible crime on these grounds, but is really just celever misdirection…though, then, isn’t all impossible crime fiction this too? Aaaarrrrrghh!!).

    Alas, the boundaries become mire blurred the closer you look at them; at the end of the day, there’s technically no such thing as an mpossible crime in the way we mean it because it has, after all, been accomplished and is usually explained in a way that is workable. Alibi Problems and Impossible Crimes are simply different exercises in misdirection — look at the scheme in Freeman Wills Crofts The Hog’s Back Mystery, where if the finger were pointed at the guilty party early on they’d be able to say “Well, that’s impossible, I was provably [doing this thing] at the time of the murder”…it’s an alibi problem that utilises misdirection to make their complicity impossible…but no-one is going to classify it as an impossible crime. Surely locked room problems are simply upping the ante in this regard, providing a further alibi by their sheer unpickableness [the motive, of sorts, in Carter Dickson’s The Ten Teacups, IIRC].

    So, yeah, I imagine there’s going to be a lot of spinning around on this one, because it’s a great question that doesn’t really have the boundaries we might like it to. Who’s next…?

    Liked by 2 people

    1. Yes it spins in circles!

      ‘Alas, the boundaries become mire blurred the closer you look at them; at the end of the day, there’s technically no such thing as an impossible crime in the way we mean it because it has, after all, been accomplished’ – This sums up what I found myself thinking the more I was trying to write about this. The point is its impossible, but of course it’s not in the end, so can the ‘impossible situation’ even act as a definer overall?

      I think what you said about both alibi and impossibility being different exercises in misdirection is really telling. I think that begins to get at some basis for this: Locked Room as a provider of Alibi or as Alibi itself is a very interesting provocation… Haven’t thought of it on those terms before.

      It would be good to think about more examples where alibi and impossibility are intertwined, or even where they might be separate? Does one always need the other? And it would be good to compare say Jonathan Creek and Death in Paradise, the first of which I of course would call an ‘impossible crime series’ and the second which I wouldn’t. What makes them different? Or what makes Jonathan Creek definitely impossible? (Apart from Ghosts Forge, I still don’t really understand how that got made.)

      Liked by 1 person

  2. I had a similar discussion about alibis and impossible a long time ago. My opinion is that a cast-iron alibi can be considered an impossibility under one, very strenuous condition: the alibi should not merely rely on witnesses (who can lie or be misled) or theater tickets, but the murderer should appear to have been physically incapable of having carried out the crime. You can do that in a number of way.

    I think Christie’s Death on the Nile is a good example of this, but also remember an episode from Monk in which the culprit was in actual coma at the time of the crime. And the solution was not bad. So I think stories like that can be considered impossible crimes.

    Hopefully, this answers your question. (again, I had trouble posting this comment!)

    Liked by 3 people

    1. Thanks Tom Cat, I think you are right about the alibi and witness link that’s really helpful. I think Salvation of A Saint falls into this category as well. And this made me think of Creek episodes that take this line: ‘Time Waits For Norman’ (they suspect is in another country), ‘The Problem at Gallows Gate’ (the suspect has been dead 2 moths) ‘No Trace of Tracy’ (the suspect has been chained up the entire time) ‘Miracle in Crooked Lane’ (the victim has already been supposedly dead for hours when they are seen by another witness) .

      I think your point justifies further my saying that much of Death In Paradise is not impossible as it doesn’t have this strenuous condition. It’s would also be difficult to pull this condition off with the whole cast of suspects being in many different places, which is what DIP seems to mainly work upon.

      Liked by 1 person

      1. Yeah, TC has — of course — nailed it there; that’s a very efficient way to apply these conditions and still provide some separation. Wipe clean everything I said before, and let no-one encourage my opinions ever again!

        Liked by 1 person

    2. Just reading back what I wrote and I really should learn to proof read my comments before slamming into that post button.


  3. I think things are summed up well by the comments above and I like the comments on the “alibi” angle. John Dickson Carr has some excellent stories where the killer had an incredibly air-tight alibi, although this never really factors into the “impossibility” of the crime. In essence, the crime only become impossible when looking back at it in hindsight. I can think of at least three examples, but I won’t mention them, because, well, that would totally give the books away.

    The one example that I can think of where alibi intersects very tightly with impossibility is It Walks By Night. On paper, it is an absolute impossible crime – a form of a locked room, if I may. Even if you ignore alibis, it is still an impossible crime, as the killer has no way to get out of the room. Ah, but the alibi is absolutely key in this case once you understand the mechanics, which is a blissful contradiction.

    Liked by 1 person

    1. It Walks By Night sounds like the perfect example. I am enjoying how these two things are more connected than I first assumed.

      My thought now is keep reading impossibles with this discussion in mind, to see how mastery of alibi and physical circumstance are used by the writer. I feel Till Death Do Us Part has some of these things happening as well.


  4. Thanks for the post. 🙂 Myself I can see the distinction between an alibi-based mystery and a locked-room mystery. The latter falls under the impossible crime category insofar as its puzzle is predicated on a physical/ spatial impossibility.

    For me, I would interpret ‘impossible crime’ quite literally: impossible for the phenomenon to have been a crime, and therefore could have been a suicide or a supernatural phenomenon. As such, I would be inclined to push an alibi-based mystery into the impossible crime category if its set-up generates such an ‘impossibility’. The story – or at least sufficient characters – must take the additional step of attempting to reframe the crime into a suicide or a supernatural event. The task of the detective, therefore, is to disprove this by explaining how the crime was accomplished.

    Hence, I would classify ‘Red Widow Murders’, ‘Case of the Constant Suicides’ and possibly ‘Hag’s Nook’ to be impossible crimes. It’s easier in the case of ‘Red Widow’ and ‘Constant Suicides’, since the locked-room element alone would qualify both as impossible crimes. But what I think is overlooked in ‘Hag’s Nook’ is that in tandem with ‘Red Widow’ and ‘Constant Suicides’, the comprehensive alibis across the range of conceivable suspects push to the fore the notion that the crime was humanly impossible – and should therefore be regarded as a supernatural phenomenon.

    In contrast, ‘Salvation of a Saint’ and ‘Hog’s Back Murder’ do not focus on how the crime was humanly impossible, and therefore not a crime; neither the supernatural element or the possibility of suicide feature much, if at all. The focalisation of the narrative in both novels is very much the sleuth’s – and neither Galileo nor Inspector French have to prove that the so-called suicide or supernatural event is actually a crime; they simply have to expose who and show how.

    Liked by 1 person

    1. Really nice thoughts JFW, eloquently put. Particularly useful is your use of the words ‘physical/spacial’ as that has been my sense in trying to describe the importance of an actual impossible occurrence for something to be classed as a locked room.

      Also really like your thoughts on how albis push impossibilities forward, and I hadn’t thought about the ‘proving against suicide/supernatural’ idea as being an essential part of a locked room mystery. In Swan Song by Crispin and also in So Pretty A Problem By Duncan this is a constant discussion, and the sleuths have to continually fight for its status as a murder and therefore as an impossibility. In fact Fen in Swan Song is accused of wanting to constantly create impossible problems, as of course to suggest that it wasn’t suicide is to create an impossibility, so it literally hangs on the detectives proclamation (and the clues we can see for ourselves).

      I wonder (can’t think of any off the top of my head) if there are any locked rooms that wouldn’t fall into the category of needing to be proclaimed super natural or suicide?


      1. Going down the memory lane of the Carr titles I’ve read, the first death in ‘Till Death Do Us Part’ qualifies as an impossible crime because of the spatial/ physical set-up, but not because it is regarded as ‘impossible to be a (human) crime’. If I recall correctly, nobody really wonders if it were a supernatural phenomenon or a suicide; Fell just gets on with it to prove who and how.

        ‘Unicorn Murders’ is an interesting title for this discussion because the implication is clearly that the murders weren’t human crimes, but were perpetuated by a mythical unicorn – but none of the characters actually take this prospect seriously.

        Liked by 2 people

        1. Two great examples, yes the multiple set ups and angles in Till Death Do Us Part solidify the fact is has to be someone, this becomes the crux of the mystery.

          Haven’t read unicorn murders yet, must get a hold of that.


  5. Whew! Excellent thoughts here, Dan. I hope you won’t mind a first-time commentator here weighing in on it.

    My take on the matter is largely similar to TomCat’s above–i.e., an alibi problem can also be an impossible crime problem, as long as the alibi creates a genuine, tangible (apparent) impossibility, a sense that, if the murderer did indeed commit the crime, he would have had to have been in two places at once. (The physicality that JFW emphasized above.)

    Even here, of course, there are caveats. Unlike JFW, I would say that “Hag’s Nook” is not, in fact, an impossible crime. That is, it does not satisfy the condition of tangible (or palpable, to use one of young JDC’s favorite words) impossibility that I set forth above. However, the technique used to create the impossibility in “Hag’s Nook,” as in Christie’s “Death on the Nile,” could hypothetically be used to create an impossible crime. That, I think, is why these two are so difficult to distinguish. They are like two magic tricks in which the effect is different but the method is the same.

    On Mike Grost’s website, he writes, “The role of the impossible crime story in the history of detective fiction seems similar to the role of infinity in the history of mathematics. In mathematics, infinity seems at first glance to be just another topic of study, one branch of mathematics among many others. But a closer look reveals the study of infinity to be the well spring of many advances in mathematics. … What the infinite is in mathematics, the impossible is in the mystery story.” Seeing the impossible as the solidifying aspect of the detective story perhaps gives another reason why the alibi tale is so similar. The alibi tale, rather than being a distinct subsection of puzzle-plotting, is itself a subsection of the impossible-crime tale, thereby indebted to it.

    I will also point out another example that differs from the physicality criterion I emphasized above: the murder in Carr’s “The Puzzle of the Green Capsule.” I would absolutely consider that one an impossible crime, but, strictly speaking, there’s nothing impossible about it. That is, all of the suspects alibi each other, creating the impossibility–but it could, conceivably, be someone else. Carr tells us why that would be highly unlikely, but it’s still possible. So, why consider this one an impossible crime and not, say “Hag’s Nook”? Part of it is, I think, what we extent a priori from a detective story. We expect a game, played fairly between writer and reader, and therefore we do not expect Carr to give us another murderer apart from our four suspects–and, indeed, he doesn’t. (The same applies for Carr’s “The Judas Window” and, to some extent, Christie’s “Cards on the Table.”) Going in with that mindset, then, the crime is therefore impossible. Again, I would undeniably consider it an impossible crime.

    I hope I’ve made myself clear and not just confused the issue more. Thanks!

    Liked by 2 people

    1. Two corrections I have to make. First, in the third paragraph, “impossibility” should be “alibi.” Otherwise, that may be awfully confusing. Second, in the fifth paragraph, “extent” should be “expect.” This is why we all need to proofread, even before writing responses to blog posts!

      Liked by 1 person

    2. Really happy to have you way in! Thanks so much.
      I loved your comment about about the mathematics/infinity angle, such a great comparison. And the impossible alibi as a subset of the impossible problem is a nice way to think about it, and I am starting to appreciate more and more the difference (and subtleties) between good alibis and good impossible alibis to create an impossible situation – as you suggested with The Judas Window and others. Would be good to create a post about impossible alibis actually, that are used well. Maybe I will!

      And you are right that ultimately we buy into the alibi problem, most of the time, because we expect fair play in the work.


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