Writing about Greenshaw’s Folly* I had noted that it hit a wide plethora of English Country House mystery tropes** but why no secret doors or passages?
It turns out secret passages are precluded by the mystery-fiction rules of fair play. Ronald Knox is generous with commandment #3 Not more than one secret room or passage is allowable. Another list of rules (though the one I can’t pinpoint at the moment) disallows for secret passages unless justified, such as a in a castle or an old house that might have one. Prohibition-era US hotels and brothels (just about anywhere) would justify them, but these are locations that smack of hardboiled detecting, not the cozy kind of which the country house mystery is a subset.
Golden age mystery fiction turns out to be an early form of adventure game, in which (in a story written consistent with fair play) the reader comes across all the clues along with the detective and thus has the opportunity to solve the crime before the reveal at the end (provided all the clues lead to a rational conclusion). It’s based on this notion that that enthusiasts and writers such as Ronald Knox and Willard Huntington Wright have assembled rules, many of which seem to be This plot device is cliche and not really fair, so please refrain from its use. This is also why such mysteries are contrived to be closed-circle, and why we indulge that Miss Marple (or Jessica Fletcher) happen upon so many murder mysteries without being the killer, themselves.
Were I to write a mystery in which I wanted to feature a country-house secret entrance, here’s how I’d do it:
Chapter One, the rotating bookshelf is introduced in a spectacle of rumbles and giggles. The children have found the rotating bookcase between the study and the conservatory, are playing with it, mostly by standing on and off the floor-turntable and pulling the secret lever (a false book on one side, a sconce on the other.) The landlord posits that his great grandfather who built the thing was terrified that people might find the house too stodgy, and added pressure-plate lights and secret doors to keep people on their toes, as it were.
Chapter Two, the rotating bookcase is reintroduced in a hide-and-seek game in which the finder counts in the conservatory while the hiders run through the bookcase into the study. One of the kids gets clever and activates the bookcase, but hops off, instead hiding behind a comfy chair in the conservatory. Sure enough, the finder is tricked by the charade, going through the bookcase into the study in her hunt, and losing track of the hider.
Chapter Three, murder! The murderer is witnessed fleeing into the study and through the bookcase. Guests in pursuit give chase into the conservatory, where it appears the killer leaped out an open window to the deadly seaside crags below.
Chapter Four, no body is found.
Chapter Late, at some point our intrepid sleuth realizes the bookshelf was activated by the fleeing killer who then hopped back off the turntable to hide in the study. While the other guests were distracted in the Conservatory, the killer modified his clothing (doffed his cloak and black murder gloves) and followed behind pretending to join in the chase.
It’s a contrivance against the rules (but a realistic one) if someone actually saw the killer’s cloak fluttering the closing bookshelf. Human brains often fill in with partial data. The lights snap on and the bookcase is turning, it’s easy to figure someone just went through it. If the same witness is particularly suggestible by a magician’s parlor tricks early in the story, that would count as setting up a red herring.
Secret entrances are discouraged because, for the mystery story, they’re a contrivance too often used to fool the reader, and are proscribed for the same reasons as are butlers (any house-servants, really), Chinamen and extraordinary poisons. So long as any of these are established early on, and given actual development, the restriction is lifted. In the meantime, I like the notion that the secret entrance is useful to the killer because it’s expected, so by using the turntable-bookshelf unconventionally he is able to make good his escape (or barely fail to do so, thanks to those meddling kids).
* Greenshaw’s Folly was a short story by Agatha Christie that was turned into the premise of a Beeb episode of Agatha Christie’s Marple, also called Greenshaw’s Folly which was a bit longer and more involved (and also featured bits from the short story The Thumb Mark of St. Peter). Greenshaw’s Folly by which the stories are named is also the Greenshaw estate and the manor, so noted because the Greenshaw landlord who built the house didn’t have much of a sense of architecture, though he was well traveled. He created a pastiche (some say an unsightly one) of different styles to suit his liking and his construction sense. It’s a fictional, smaller Winchester Mystery House.
** According to Thomas Godfrey there are specific conventions that should be followed for the setting of a Country House Mystery: The house should have character (pleasant, dreary, austere, ornate). Secrets, ghost sightings, servants and an unreliable telephone system help make the place fun for the reader. There’s a lot of cross section with the gothic horror setting.