Something that has always fascinated and puzzled me over the years is the close relationship between mystery (a supposedly realistic genre, at least according to critics) on one hand and imaginative literature on the other, be it of the sci-fi or, more specifically, supernatural kind. Not only have they often overlapped, but many authors have dabbled in both, and became masters in both fields. It may have to do with mystery fiction's extreme plasticity - you can set a crime almost anywhere, anytime - as the prolific subgenre of historical mysteries demonstrate. But I can't help thinking it may also have to do with our favorite genre's deeply ambiguous nature. Even in its most realistic-looking guises, mystery is a fundamentally artificial genre relying on rare, if not downright improbable, combinations of events and characters that have themselves little relation to everyday reality. Most true crime is trivial, uninteresting but on a philosophical/sociological level - and the lives and personalities of those investigating it are not the stuff of novels. It's possible to write good mainstream fiction about nothing happening to nobodies, but a crime novel that would deal with uber-ordinary crime solved by uber-ordinary detectives would be a yawn-fest committing the genre's gravest offence: boringness. All genre fiction is about being interesting and captivating, and is thus fantasical at the core; mystery is no exception, even though it goes to greater pains than others to hide it.
But back to the special relationship I evoked at the outset of this post. It goes back a long way - not only is Poe - rightly or not, that's another question - a patron saint of mystery fiction, he always serves that function for sci-fi ("Hans Pfaal" is often regarded as an early specimen) and supernatural fiction, especially horror. Had Poe not existed or stuck to poetry, this blog might not exist. Also, the lines between the genres took a long time to be delineated - the Victorian and Edwardian eras were home to rationalists like Holmes or Thorndyke as well as to specialists of the paranormal like Carnacki, Flaxman Low, or John Silence. Better still, the literary techniques of mystery fiction were sometimes applied to stories of the supernatural; Arthur Machen's The Great God Pan for instance is structured quite like a detective story and H.P. Lovecraft's later Call of Cthulhu makes effective use of a "backwards" structure (from the effect to the cause) similar to that of the mystery genre - and the protagonist acts like an investigator. Conversely, ghosts (real or forged) hypnosis and futuristic weapons were long a fixture of mystery fiction, much to the ire of purists like Mgr. Knox or S.S. Van Dine. It took the advent of hardboiled, and the subsequent call for greater realism in the genre, for the lines to be settled - mostly. They seem to have remained porous somewhat longer in Britain though, as demonstrated by the group of writers I affectionately call the "British Weirdoes" which comprises the likes of Mark McShane, John Blackburn, Colin Wilson and the mother of them all, Gladys Mitchell. (The most recent example of that school I can think of is J.H. Wallis' 2002 novel Dancing With The Uninvited Guest)
The proximity between mystery and "imaginative" fiction is, I think, more than just a matter of occasional meetings. It's one of kinship; mystery itself, especially in its most traditional incarnations, being a branch of imaginative literature. It's my own interpretation, not a minority view and open to discussion, but I do like it. I report and you decide; feel free to disagree and let me know your opinion on the matter.