Not more than one secret room or passage is allowable. I would add that a secret passage should not be brought in at all unless the action takes place in the kind of house where such devices might be expected. When I introduced one into a book myself, I was careful to point out beforehand that the house had belonged to Catholics in penal times. Mr. Milne’s secret passage in the Red House Mystery is hardly fair; if a modern house were so equipped – and it would be villainously expensive – all the countryside would be quite certain to know about it.
Of everything Knox sought to confront in his decalogue, this is the one rule which I imagine requires the least defence or explanation. Secret rooms and passages can have their place, but too much of anything becomes wearisome when it is used — as it has been countless times, in too many novels, short stories, and movies to name here — to repeatedly explain away or allow criminous deeds. If four people disappear from the Mysterious Cursed Room in your family mansion, chances are it’s a secret passage that’s enabling such a thing. If people disappear from two different rooms, each with a secret passage of their own…well, come now. And as the number of rooms from which our Victorian Villain may snatch the unwary multiplies, so diminishes our interest in these answers when they’re reached.
So, what to say about Rule 3?
Firstly, I suppose, that — while the secret passage suffered something of a tailing-off in popularity as crime fiction lowered itself from Gothic castles populated by looming, glowering Obvious Bad Types and took up residence in the vicarage, the boarding house, the train carriage — the secret room never really went away. It may have reduced its stature to a mere nook (hidden beneath the floorboards, say) in which stolen goods may be stowed or a killer may escape detection, but as such it allows a certain degree of ‘Purloined Letter’-style oversight to excuse its efficacy. and retain its “secret” nature Nevertheless, the most effective deployment of this principle — ‘Hot Money’ (1939) by Carter Dickson, say, or (at a push) ‘The Scientist and the Vanished Weapon’ (1966) by Arthur Porges — works wonders when ingenuity is brought to it rather than seeing the “secret room” as a literal room.
And so, in its own way, Rule 3 casts a light not so much on the literal interpretation of these ideas, but on the myriad ways that GAD would take the essential principle of something and adapt it over and over with a fecundity that still renders these ideas so compelling all these years later. When even Norman Berrow — who loved a secret room or passage as most of us love the sun on our skin — takes the secret room trope and plays with it enough to hide a room inside a room, you know your concept is going through some revelations. And so as the idea of a hidden room became a hidden compartment (not really all that revolutionary, doubtless many a scandalous letter was secreted in many a Gothic desk over the years…) the revolutionary principle picked up by GAD was surely not to redefine what “room” meant as, more tellingly, to redefine the nature of secrecy.
Declaration is covered in Rule 8, and so still ahead of us in this meander through Knox, but arguably the defining principles of GAD reached their pinnacle when the author boldly shows you what you need to know and yet you fail to appreciate it: the butler squinting at a calendar, an unopened letter on a desk, a key disarranged from the pocket of the victim: in their respective books, they tell you a lot more than it might initially seem. The talent of GAD was in getting the reader to see the significant as mundane and vice versa, and so the idea of a secret passage or room becomes in many ways a challenge to the reader to interpret what they’re told, and to recognise the significance of that event when it happens (we can’t, after all, go about tapping on the walls or measuring corridors — and any floorplan that goes to the effort of providing exact measurements of space is, well, tipping its hand somewhat). Something is secret if it is hidden and GAD, after all, revelled in flaunting the recondite under the noses of those who watched.
To pick examples from outside the Golden Age so as not to spoil too much: there’s an argument that Dr. Grimesby Roylott (second-best name in the canon) utilises a secret passage in the Sherlock Holmes story ‘The Adventure of the Speckled Band’ (1892), since we know there’s a passage of sorts, and yet do not intuit its meaning. Equally, out the other end of the era, Murder in the Crooked House (1982, tr. 2019) by Soji Shimada makes it plain for all to see that a ‘secret’ passage is very much at the heart of that novel’s seemingly-impossible stabbing…and yet, in brazenly declaring the means by which such access is made, the misdirection — or perhaps overstatement in this case — would be sufficient to hide its presence from the majority of readers. I’m being more careful around GAD examples here because the risk of exposing too much in terms to well-judged public secrecy, but you could doubtless cite a great many cases in the appropriate time period where the same was applied.
And so what we also have here is the exposure of the lie commonly put about, as evinced in the introduction to this series, that the Knox Decalogue was something taken especially seriously by authors at the time. Knox proposes a moratorium on concealed passages and rooms, and GAD responds with just about every form of secret, concealed, hidden, fully-on-display room, cranny, space, opening, corridor, alley, and crawlspace the human mind could devise. And people say that Carolyn Wells and Wadsworth Camp made no contribution to the pinnacle of GAD…
The only other thing to discuss, then, is poor A.A. Milne getting yet another kicking. I’m not entirely sure what to make of Knox’s assertion that the passage in The Red house Mystery (1922) is “hardly fair”. It’s been a number of years since I read it, but don’t they spend, like, a full chapter discussing the various implications of the passage and its location? Such as, it can’t originate from any but the ground floor or cellar, and that it would be unlikely to be on the “wrong” side of the house since the digging it would require navigating back past the foundations, etc? And — though, again, it’s been a number of years — isn’t the fact of the exit outside the house being in a particular place used to explain how one witness sees someone who must have come out of the tunnel but another doesn’t, since they would have passed them while in the tunnel (or similar — I’m not sure that book is so well-read as to risk spoilers)? That’s no simply dropped in out of nowhere as used in the chain of reasoning to support a conclusion…so in what way is it “hardly fair”? Dammit, man, define your terms!
Hmm, that appears to be it for this week. Not gonna drag this out needlessly, but rest assured that plenty of tedious 3,000-word essays remain in the wings for when I pick this up again sometime in 2020. The reader is fore-warned…