#717: Reflections on Detection – The Knox Decalogue 4: Undiscovered Poisons

It was, by pure chance, this time last year that I started a series of posts examining Ronald Knox’s Ten Commandments for Detective Fiction rule-by-rule and, well, we’re back to continue what I started. Woo?

Here’s the list of links that will gradually fill in as this undertaking progresses:

And here is Rule 4 in all its glory:

No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end. There may be undiscovered poisons with quite unexpected reactions on the human system, but they have not been discovered yet, and until they are they must not be utilized in fiction; it is not cricket. Nearly all the cases of Dr. Thorndyke, as recorded by Mr. Austin Freeman, have the minor medical blemish; you have to go through a long science lecture at the end of the story in order to understand how clever the mystery was.

In essence, this rule covers two extremes: don’t stray into pure fiction, and don’t lean so far into fact that you stop writing fiction and start writing a textbook. Knox, fundamentally, wishes to admonish the writer who is too keen — perhaps too lazy in their writing — to do either, and the reason for this, while I shall expound upon it today, can essentially be boiled down to a single one: ignorance.

Broadly speaking, I’d suggest there are three kinds of ignorance at play here:

1: The Reader’s Ignorance of the Clues

The detective novel, in which the reader is given the clues and yet remains in suspense about the eventual outcome until the author reveals it, relies on the reader’s ignorance of those clues as clues until the moment of revelation. Thus, while your clever reveal that the innocent-seeming archery teacher was in fact the Great-Aunt’s stepsister’s adopted son Tony, and this reveal comes about from recognising that arrows intended for flights of between 20 and 100 metres are feathered from the genus Aquila but he was preparing for the annual Scouts’ archery competition 25m shoot with the feathers of a hawk eagle (of the genus Nisaetus)…well, the long-winded essay on bird gena and arrow flight lengths delivered seemingly at random two-thirds of the way through is going to stick out like a sore thumb (for anyone worried I’ve just spoiled the world’s weirdest mystery, this example has been wholly invented by me).

Which is not to say that simply spotting that something is relevant is the same things as knowing how it’s relevant — I can point you to several novels in the genre where I know a clue has been given to me but I’ve no idea what it is or how to use it — but, generally, I think we prefer to know that we’re ignorant of being informed rather being informed of our ignorance. This can often be more of a difficulty with short stories, where the limitations of space often require some narrative handbrake turns to enable the appropriate revelation or understanding to be wedged in, and it makes it all the more frustrating when you know it’s being done in a novel, as if there’s weren’t 250 previous pages where a few subtle hints could have been dropped.

Which brings us to:

2: The Reader’s Ignorance of the Principles Involved

In some cases, the reader is ignorant of the clues because the clues themselves are the precise kind of thing one would expect to be ignorant of (such as ending a sentence with a preposition). I don’t think Knox is decrying scientific esoterica but is fine with utilisation of the subtleties in brush fibres of Aboriginal art from the Iberian peninsula in the third century A.D., but rather he’s saying that you’re not really playing the game in the manner intended if it’s unreasonable — a subjective standard, to which we shall return — to expect your layperson reader to have knowledge of an idea only a career anthropologist, say, would possess.

I understand that if I drop a rock from a great height it will accelerate towards the ground on account of gravity and, if going fast enough, will kill someone if it strikes them on the head. This, it’s not unreasonable to say, is commonly understood. But the fathom the precise method of murder in Agatha Christie’s debut The Mysterious Affair at Styles (1920) requires a knowledge of chemical reactions which we’re assured in the book is widely known and easily available to check (the two, note, are by no means the same thing)…the assurance feeling like a hasty attempt to shore up the disappointment of our never really being able to solve this one. To take a modern update of this, Oscar de Muriel’s The Darker Arts (2019) relies on a scientific principle that won’t be recognisable from the context in which it is presented, and then in the afterword he more or less says “No, this is a thing! Look it up on YouTube!”…at which point his editor should have maybe put the manuscript aside and enquired how things were going for him at home.

Now, of course, what is a layperson’s awareness of science, art, anthropology, etc? I’d suggest that the average person on the street today knows more about general, loosely hand-wavey Science than did the average person of the 1930s, and so the degree of explanation we deem necessary today might be significantly reduced and so seem at times redundant to we Men of the Future (Knox is, I think, being more playful than admonitory in his dig at Freeman). Before we get too snooty at the ignorance of our forebears, though, elements of this awareness also apply the other way round: today we’d likely cry “Foul!” at the story where a young man is determined to be guilty of a murder because he’s wearing the wrong type of shoes to take his victim to a public dance hall, but it’s actually a rather lovely and subtle clue. My point? That perhaps the universality of understanding is found more in experience than it is in learning, common experiences may be considered safer ground — that one requires glasses if short sighted and wishing to read the date on a desk calendar, say — than anything axiomatic.

The baffling-to-me popularity of the U.S. medical drama House (2004-12) — where, essentially, millions of people who knew nothing about medicine watched actors spout lines about obscure medical conditions that the audience has never heard of, couldn’t recognise, and would not remember once the credits rolled — shows that standards of acceptance are wildly variable between media, too, but there’s no accounting for taste and you’re arguably wasting only an hour of your life on House to be told something you didn’t know, versus maybe eight hours on a book for the same result (though at this rate you could have read 16 books rather than watching every series of House…and probably learned something interesting along the way). The net result is the same, but the delivery might be key to how willing we are to overlook these problems.

This in turn leads us to:

3: The Author’s Ignorance of Reality

In a recent episode of my In GAD We Trust podcast — I forget which one, because I am horrible at self-promotion — I suggested that the apparent lack of interest displayed in the dying moments of the victims in so many GAD novels could be down to the writers simply not knowing how such a death would manifest itself and so not wishing to accidentally misrepresent it and give false clues (describing death by strychnine, say, as the quiet passing of a man injected with opium). And this brings us full circle back to our starting point, because if I’m ignorant that something is a clue, and I’m ignorant of the principle you’re telling me would manifest in that way, then it damn sure better manifest in that way and actually be the clue you say it is.

Exceptions can be made — if you’ve got a universe where certain poisons follow different rules, go for it…but make it clear that we’re getting some removed-from-standard-reality shenanigans — but the problem faced by GAD in particular and crime fiction in general is that an awareness of what is and isn’t permissible within the tropes we encounter will be achieved by even the most non-specialist reader (!?) if they encounter them in enough books. As such, the writer’s ignorance or misrepresentation of what they’re doing can cause huge problems for the validity of their presentation if it’s not in keeping with what is known to be the case elsewhere. Consistency is key, and a writer ignorant of what they are explaining is far, far less acceptable than a reader being ignorant of what they are required to know.

Over the weekend, I tried to read The House of the Arrow (1924) by A.E.W. Mason and didn’t fare too well, but the following really stuck with me:

Here is a report, Monsieur, from the doctors. Because it says that no trace of the poison can be discovered, you can’t infer that a poison was administered which leaves no trace. You never can prove it. You have nothing to go upon. It’s all guess-work, and guess-work which will keep us living in a nightmare.

A.E.W. Mason, The House of the Arrow (1924)

In the same way, a writer who claims, say, that strychnine induces a nice peaceful death and never explains this discrepancy is leaving the reader living in a nightmare where the various ‘clues’ we may be required to use leave us equally guessing at their possible inclusion, relevance, and accuracy. Any detective novel where the rules and workings of the universe are not clear — even down to the feelings and relationships between characters — equally leaves the reader with “nothing to go upon” in the same way that overly esoteric reasoning leaves the game beyond their reach. The author should, surely, do their best to know what the audience knows…and the surest way towards that end is to try to include the information that is needed. And if that can’t be done in a subtle way, sometimes what you get is a bad mystery.

As with virtually everything I dedicate time to in my life, there is the question of really how much any of this actually matters. If the aboriginal population of the Iberian peninsula did their painting with horse-hair brushes in 3 A.D. and you say they used fox-hair because you included fox-hair brushes in your novel…so what? To a hardy few this might be evidence that the author knows not whereof they speak, but then it’s clear from reading even a handful of GAD novels that most authors threw out proper procedure and accurate representations of crime-solving in the service of plot from the get-go. If we wanted realism we’d read a newspaper. The one thing you can arguably guarantee about any audience is that most of them are non-specialists in most disciplines and have picked up your book for a bit of fun. Maybe making it fun is enough — there are plenty of books you couldn’t get me to read past page 20 for any amount of promised fidelity to the arcane working as its core.

37 thoughts on “#717: Reflections on Detection – The Knox Decalogue 4: Undiscovered Poisons

  1. I do apologise for the non-sequitur comment – but I clicked on the link to your review of Muriel’s ‘Darker Arts’. And it occurred to me how your endeavours to recommend an impossible crime novel to TomCat as well as discover an excellent mystery novel that’s independently published haven’t been entirely – or even remotely – pleasant journeys. 😑 Apart from the discovery of Byrnside’s novels. 🤩

    The masochism of blogging!


      • Being able to enthuse about Byrnside’s work and get people interested in and reading him has been the highlight of this modern/independent impossible crime undertaking, no doubt. But they’ve all been worth reading, and I’d say very little of the time spent on any of it is to be regretted.

        I’ve said it before, I’ll say it again, I’ll keep saying it: I’d much rather read something and know I find no merit in it than spend my whole life avoiding it because of some baseless supposition and so never actually find out either way. De Muriel might have been exactly what I was after, as might Andrew Mayne, J.R. Ellis, or any of the modern authors I’ve read while doing this. They weren’t, I was able to get my frustrations off my chest and move on, and now that incessant curiosity is salved and I can go a-hunting elsewhere.

        And, c’mon some of these have been good: The Real-Town Murder by Adam Roberts, the best of Robert Innes (Ripples, Reach, Flatline, the long-game played in that series), Hard Tack by Barbara D’Amoto. Yes, there’s more inept prose and plotting elsewhere than you can shake many, many plot-holes at, but you don’t understand the relief of knowing it’s bad and the pressure that lifts from my brain.

        Rest assured, my mental health is precarious enough that if I got no enjoyment from doing this I’d stop bloody doing it!


  2. Again prefacing this with the point that I consider the whole idea of rules in regard to detective fiction a matter of conceptual inapplicability (borne of taking the playful metaphor of the genre as competitive game too seriously and literally), I think this particular “rule” is— like the prohibition on the supernatural, secret passages, and several others— merely a reflection of the expectation that the puzzle will sufficiently indicate the solution. Though Knox disallows hitherto unknown poisons and long scientific explanations, I think he would recognize that the primary problem is with poisons unknown prior to the denouement, or long scientific explanations not given until the denouement.

    If we think of the detective story as an equation (a much better analogy for the genre, if we’re going to allow one that removes the concept of art), with all that is found left of the equals sign constituting the the puzzle and all that is right of it the solution, the expectation is that there should be nothing of significance on the right side that was not given— or could not be inferred— by that on the left. Thus, it is not the fictional aspect of an unknown poison that is objectionable, but rather that it is offered in the solution without qualifying as something the reader knew about or should have known.

    Admittedly, some readers might object to the use of the fictional poison Glomavene as a murder weapon, but most would only object to the use of the substance if it were not somehow introduced and explained as fatal to humans prior to the denouement (which is in itself a good reason not to use Glomavene because, as you mentioned, such an explanation as that “before the equals sign” usually allows little or no opportunity for related surprise). Though it’s from another mediocre Chesterton story, far better to use gravity, as it’s something we’re all knowledgeable about, but do not necessarily associate with murder (outside of defenestration). There is, of course, a minimal level of denouement-introduced specialized knowledge that readers will accept and even enjoy (oh, a Cyrillic H looks like our N? Neeto!) but as employed as the core of a solution, it disappoints because it does not allow for demanded sense of sudden retrospective illumination (that is, it provides the “Oh!” but not the equally demanded “of course!”).


    • I’m pleased to see that we agree in so many aspects, Scott — I’ve wanted to get back to this more discussion-based style of post for a while, but the rigours of 2020 have kept me in a safe box of reviews for the majority. Thankfully there’s nothing too controversial in the forthcoming — No Chinamen indeed! — so it’ll be nice to just air some views and see where others stand.


      • Yeah, I actually think No Chinamen either falls under the same expectation (if the Eastern character turns out to be the culprit) or the expectation that the solution will account for all aspects of the puzzle (if he doesn’t). And I’m also assuming that the latter was more common and irritating.


    • Isn’t this sort of ‘rule’ present in science-fiction and fantasy literature too? As in, the author constructs a world where people flying is the norm which the reader accepts. But then if the hero out of nowhere suddenly starts shooting lasers from his eyes (pardon the bad example) he is breaking the in-universe rules. Ultimately all the reader asks for is ‘fair-play’.


      • I’d completely agree — and, indeed, it was this precise thinking that prompted Isaac Asimov to write his Asimov’s Mysteries (1968) collection: in any genre, it’s crucial that the reader knows what is allowable from the characters and the setting, or else the book becomes increasingly difficult to engage with.

        The books I have read where the precise nature of the ‘rules’ is left deliberately unclear — The Dead Mountaineer’s Inn (1970) by the Strugatskys springs immediately to mind — are among the more disappointing of my reading experiences. I mean, I’m no fan of the writings of Galdys Mitchell, but at least you knew what type of story you were reading. The ‘rules’ and the reader’s awareness of them is so, so important.

        And, yes, before anyone points out that not knowing the rules can often add to the fun, I’ve talked about that here and acknowledge that sometimes — sometimes — the unpredictability can be a distinct advantage. But those times are few and far between, and require the sort of skill in writing one sees very rarely (c.f. the excellent Inside No. 9 TV series).


        • There’s a Hindi movie called Talaash made in 2012. Beautifully made and highly recommended. I’ll try talking about it without spoilers. It was marketed as a mystery movie. And then something else happened. Most people were annoyed. But I bought it completely because the makers had put clues through both writing and atmosphere that something else was going on. It was fair.


          • I may have over-egged the pudding. I do completely understand why people complained about Talaash. I am just saying I somehow bought the story. Sometimes not playing fair can work.


          • The Julianne Moore movie where her daughter vanishes and no-one has any memory of her is another sudden switchover in genre…and one that doesn’t work, in my opinion. I feel writers have to pick their themes very carefully when doing that kind of thing: there’s undoubtedly a lot of crossover between different genres, but that doesn’t mean a story needs to veer wildly through as many of them as possible…!


  3. Re. the author’s ignorance:

    I am amusedly reminded of James Yaffe’s rather lovely short story where the murderer gets rid of the murder weapon by blowing air into a balloon, attaching the weapon to it and then letting it sail away into the blue.

    Not even the editors of EQMM – Fred Dannay, in fact – caught that hilarious mistake before publication.


  4. Very pleased to see the The Knox Decalogue posts back up and running. Will you be doing one each Tuesday in November?
    Though also a bit anxious as I noticed your upcoming review title. Will you like? Won’t you like it? Not sure any bookie would be giving good odds, given your recent dislike of The Woman in the Wardrobe – a seemingly sure fire winner.


    • The plan is, yes, to get rules 4, 5, 6, and 7 done over the four Tuesdays in November — always assuming, that is, I need only a single week for each one — and to then do the remaining three…maybe next November? 😄

      As to Blue Murder by Harriet Rutland, I’ve just this moment finished reading it and definitely have some feeling about it. As to what those feelings are…well, come back on Thursday to find out 🙂


  5. Well, JJ, I was going to say something but Scott beat me to it . So read his comment twice at the very least 😋 There’s nothing stopping a writer, for instance, from devising a clever mystery set in the far future as long as the technology employed is clearly explained beforehand.


  6. Excellent breakdown of the rule. Scientific explanations (be they succinct or long-winded) rankle less the farther they are from the end summation, although there’s nothing like a dry lecture in chapter 1 to stall the narrative immediately.


    • I think I feel differently about this. I don’t feel the distance from the end affects my acceptance, only that everything comes before the “equals sign.” That is, once the denouement commences, no new information is permissible— only new interpretations.


      • Technically, I’d agree with you — before the summation is the bare minimum. I would say that a complicated scientific explanation works better when it’s introduced earlier. Certainly, an invented poison should be introduced before the half-way mark. I know you have issues with the term “fair play”, yet it’s an idea that writers hold dear–or at least should hold dear. Inventing a new poison and first mentioning it in chapter 10 is play most foul. It would break the “reality contract” (is there a better term?). The reader discovers too late that this world differs from the one he had been experiencing in the first 10 chapters.


        • Well, I’m as sensitive to disappointment due to paucity of clueing as the next fellow. I suspect that what pleases or disappoints me in a detective story solution is just about the same things that do so for you and others— my subjective expectations are similar to everyone else’s. What most reader’s consider unfair are the same things that make a story unsatisfactory for me. I just make a strong distinction between satisfaction and “fairness”— I simply don’t believe that a puzzle plot solution can be accurately said to be OBJECTIVELY sufficient or insufficient.

          My beef with The Crooked Hinge is that its ultimately-presented solution is too thinly-clued to seem satisfactory or inevitable to me. To ME. What I object to in the term “fair play” is the clear implication of an abstract, objective standard. This threshold of “all the clues necessary to solve the mystery” which no one has ever clearly delineated (probably because it is not possible to do so, IMO). Because if “fair play” and “all the clues necessary” aren’t reference to a standard outside our subjective creation— if things aren’t objectively fair or unfair— what do those phrases mean? I might say that a certain soup isn’t salty enough for me, but no one of intelligence argues for an objective standard of satisfactory saltiness.

          Hell, no one even goes to the trouble of attempting to explain what it means to “solve” a mystery (does guessing correctly on a hunch qualify? How about having a strong sense of probability based on the clues? Is total deductive provability necessary— and if so, must it extend to all aspects of the solution [for if it does, one must write off all solutions including motive]?).

          I think my difficulty is conveyed in the humor value of the Emperor’s claim to Mozart of “Too many notes!” It’s the effort to explain subjective satisfaction in objective terms, and particularly an objective term based on an inapplicable metaphor. If the Mona Lisa were a stick figure, we might call it lousy, but we wouldn’t call it “unfair.” If “Rhapsody in Blue” consisted entirely of the same two-bar phrase, it would no doubt be critically derided and decidedly less popular, but we wouldn’t call it “fair.” The only reason we use the term “fair play” in reference to detective fiction is an allusion to the playing of competitive games— in which “fair play” is both applicable and necessary. But the competitive game metaphor of detective fiction— while colorfully evoking the ludic aspect of engaging in it— actually holds no more than calling a camel an airplane because people can travel great distances on it and are far from the ground when doing so. At a very fundamental level, a detective story is quite distinct from a competitive game for several reasons— and the necessity for objectively measurable fairness is one of them.

          My work too has been described as “fair play” and containing “all the clues necessary.” And it’s important to me that it will give people the sense of being satisfactorily sufficient in that regard. But that’s just a “sense.” For, while I feel I have a good idea of which clues would be most missed if removed, I couldn’t delineate at which point “all the clues necessary to solve the mystery” would no longer be there— because I don’t believe it’s an objectively definable phrase, as much as it’s usually bandied about as if it were. And I think that the drive of Knox, Van Dine, and others to codify rules for the genre was merely an attempt to address the shared expectations of readers— which I believe number three (the expectations, that is, not the readers!)— in a form that is (inaccurately) presented as exact and scientific.


      • Then you need to find an offhand way to demonstrate it as far away from the case as you can. Whfg gb hfr zl bja rknzcyr orpnhfr vg vf fb erprag: Jura Jvyyvnzf phgf bs Oebjavat’f svatref, V (cnvashyyl) vapyhqrq gung gurer jnf irel yvggyr oybbq orpnhfr gur cerffher jnf tbar. Yngre, gur fnzr cevapvcyr fubjf hc jvgu gur unaqf. Vg jnfa’g greevoyl arprffnel orpnhfr vg vfa’g bofpher fpvrapr, ohg lbh pna qb gur fnzr jvgu lbhe bofpher fpvragvsvp cevapvcyr. Svaq n jnl gb qrzbafgengr vg gung vf bssunaq be angheny naq lbh pna hfr vg sbe gur fbyhgvba. Nqzvggrqyl, uvqvat guvatf vf qvssvphyg. Try and make it a story someone tells.


        • Good advice, thanks, though thankfully I have plenty of time — it’s not like I’m the one with any expectation on me to write another blistering impossible crime novel in the next twelve months…


  7. I love how your dissection of the rule shows it to be so much more than it appears to be, but am I reasonable to say that this may be the rule that is also easiest to nod your head with when simply taken at face value? More so than any of the others (although I’ll probably be convinced otherwise), I think you can read this one and say “yes, never do that.” I mean, to read a 200 page novel and then get that as part of the solution… Yeah, you wouldn’t want a secret passage at the end either, but I think we’ve seen counter examples that show the obvious nuances in that one.

    I am amused by the variance of symptoms that you get in literature for poisons. There’s quite a bit of dropping dead after a few spasms, which would almost never be the case, from what I recall reading in Murder Ink.


    • I do wonder if part of John Rhode’s falling from grace and public awareness is on account of his love of some obscure science stuff — I’ve not read enough to say for sure (he has, after all, fallen from public awareness and is only moderately in print), but the concepts the resolve, say, Death Leaves No Card and Mystery at Olympia show that he wasn’t afraid to dump some technicality on you at the death. He was also a very entertaining writer, however, so I do hope that such potential foul play isn’t what held against him.

      And, yeah, I think all of these rules are pretty difficult to disagree with — Knox’s list is far better than Van Dine’s in that regard, but then one feels Knox understood the genre better than Van Dine (and is being a little less pompous about it as a result).


  8. “Over the weekend, I tried to read The House of the Arrow (1924) by A.E.W. Mason and didn’t fare too well”

    No, don’t tell me you’re not an A.E.W. Mason fan. That would be heresy!


    • I’m not a fan based on the first half of The House of the Arrow, certainly. He’s long on melodrama and short of cohesive plotting…not a mix I tend to enjoy.


      • I feel there’s a lot of good “destination” stuff in HOTA (i.e, clue payoff), IMO, but I don’t know if your consider it good enough to justify what it takes to get there.


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