Thus , if he has a complete set of the works of Mr. John Drinkwater , bound in vellum , but enough .sx We cannot go into details ) , and the next thing to decide is his name , rank , title , occupation and character .sx Here would be plenty of scope for originality if it were not for the following considerations , which limit the choice of victims most rigidly .sx It is , of course , obvious that the house-party consists of one murderer and a number of suspects , each of whom might very well have done it .sx The more suspects , the greater the confusion .sx And as each of them has to have a separate motive for killing the man , it follows that the number of suspects depends entirely on the number of motives which the author can invent .sx But ( this is like Euclid ) it is universally admitted that more people would like to kill rich men than to kill poor men .sx Therefore the richer the victim , the greater the number of motives , and therefore the more suspects , and so the better problem .sx The inexorable conclusion is that the unfortunate owner of the country-house library must be a multi-millionaire , a Colossus of Finance .sx In fact , this last expression is invariably used in the same paragraph which describes his skin of a curious parchment-colour and his torpedo-shaped beard .sx The multi-millionaire automatically adds the motives of the Forged Will , the About-to-be-Disinherited Heir , the Revengeful Employee , the Ruined Competitor , the Old-Pal-of-Early-Days who was sent to the Breakwater on false evidence , the Life Insurance Policy , the Financing of Foreign Revolutions , the Stampeding of Wall Street by making it look like suicide , and the Unset Diamonds in the safe .sx No novelist in his senses can afford to ignore nine clear , separate and generally accepted motives , all of which can be simultaneously introduced by the simple words , " Sir Otto was a veritable Colossus of Finance , " or , in the case of the slightly less high-brow writers , " Sir Otto was literally a Colossus of Finance .sx " Even his appearance and age are predetermined .sx He must be old enough to have shaken off all traces of a murky and obscure past , but not so old that he is no longer a menace to somebody's matrimonial affairs .sx Otherwise the Jealous Husband motive is lost .sx This would place him at about fifty-five , and would make him good-looking in the exotic sort of way that appeals to women but not to straight-living old Wykehamists and Cavalry Colonels .sx Probably he would have iron-grey hair , and if , in addition , he had square shoulders and an immensely powerful physique , he might well have thrashed a revengeful poacher a few days before his death .sx He must certainly be either a man of sudden , uncontrollable gusts of tempestuous rage , or else a quiet , patient man who never forgets or forgives an injury , and is prepared to wait for thirty years to get his own back .sx It is even possible for certain kinds of authors to combine the two sets of qualities and make their dead millionaire a cross between a wild-cat and a spider , but this is not considered quite the thing in the best literary circles .sx The next step is the manner of the killing .sx The big , iron-grey , torpedo bearded multi-millionaire is lying dead in his library , and the doors andwindows are locked , of course , from the inside .sx Flow was he killed ?sx There are two well-defined groups of methods .sx The first consists of the pistol-shot ( which was mistaken for a car backfiring and inevitably means a daylight-murder ) , the blunt instrument , the stiletto , which introduces the mysterious Italian who called two days before to sell vacuum-cleaners , the dose of poison and strangulation .sx The last is comparatively rare , as authors fight shy of a process which involves expert witnesses and the effect of bruises .sx upon the tissues , and what may be described generally as Sir Bernard Spilsburyism .sx This group makes up the straight or legitimate methods of murder .sx They may be used singly or in pairs ; thus Sir Rudolf Wolfgangheimer may be either stabbed in his library or else poisoned in the railway-buffet at Wolverhampton , and his body brought secretly to his country-house , deposited in the library and then stabbed in order to make things more difficult for everybody .sx Or he may be shot with an automatic pistol in , a flat in West Kensington and subsequently battered about the head with his own library poker .sx The second group includes the more fanciful , and therefore less legitimate , methods .sx It is not playing fair to the reader to kill your man by passing a Z-ray through a helium plate in such a way as to asphyxiate all tall dark strangers within fourteen yards of the instrument ; and so , for our purpose of , determining the limits which the intellectual problem-story imposes upon its creators , this group can be ignored .sx It is sufficient to note that in this group falls Murder by Hypnotism , by Auto-Suggestion , electric shocks , mysterious death-rays , the passing of highly-trained snakes down bell-cords and the blowing of poisoned soap-bubbles through ventilators .sx These can all be dismissed as belonging to sensational , not intellectual , literature .sx After the murder is discovered , the immediate procedure is for the most competent man in the house-party , usually the ex-captain of Irregular Cavalry who had to leave the Service for cheating at cards , to shut up the library , put a guard upon the door , forbid any member of the household to leave the house , and telephone for the police .sx In due course the County Constabulary arrive , bringing with them Inspector Jones ( or Brown or Smith or Robinson ) of Scotland Yard , who happened to be in the district on another case at the moment .sx The County Constabulary , always eager and proud to work with Headquarters and itself seeking only a quiet life , hands the case with alacrity over to the great man , provides him with sub-ordinates , motor-cars , maps of the district and local time-tables , and retires from the scene .sx We have now come to a most important ingredient in the recipe , the character of the Detective .sx In the first place , it is highly desirable that he should have a character of some sort , even if it only consists of an assortment of minor mannerisms .sx For reasons that we will go into later , it is practically impossible for anyone else in the book to have a distinguishable character , and it is therefore of the greatest importance that something should be done , however trivial , to give the detective some sort of individuality .sx Let him collect match-box lids , let him have a trick of talking to .sx people over his shoulder with his back to them , let him have a quaint stutter when saying Darwinism or Botticelli , it doesn't matter what it is so long as we have something to remember him by .sx Next , the detective must be a professional .sx The long reign of the amateur is over .sx No one will swallow him any longer and Scotland Yard has come into its own .sx The reason for this is sociological .sx In this country everyone knows that the status , efficiency , technical knowledge and organisation of the London Detective Force has been raised within the last twenty or thirty years to an extraordinarily high standard .sx Conan Doyle , in the 'nineties , could describe the pride of Scotland Yard as a " lean , ferret-like man , furtive and sly-looking , " and the readers of the 'nineties presumably saw nothing incongruous , let alone slanderous , in the description .sx But that would not pass for an instant nowadays .sx The intellectual murder-story demands realism , and therefore out goes the amateur , out goes the Bow Street Runner , and in comes the modern professional , shrewd , painstaking , untiring , and supported by platoons of photographers , finger-print experts , soil experts , foot-print experts , record departments and all the mighty organisation which , as every reader instinctively knows , exists on the banks of the Thames .sx The only surviving amateur in fiction of any real fame ( not counting , of course , Father Brown , who is in a category all by himself ) is an ex-professional , M. Hercule Poirot , created by Mrs. Agatha Christie .sx All the rest are professionals .sx These , again , are divisible into two groups , one type necessitated by the plot in which the reader has a chance , and the other in which the reader frankly has no chance .sx This latter group consists of policemen who steadily and stolidly follow up every infinitesimal and minute clue on the chance of being led somewhere in the end .sx A classic example of this group is Inspector French ( Mr. Freeman Wills Croft ) and a classic example of how this group goes to work was given in real life in the Rochester Row murder a few years ago .sx A woman's body was found tied up in a brown paper parcel in a railway cloakroom , and one of Scotland Yard's avenues of exploration consisted of sending policemen to every shop in London that sold string and brown paper on the chance of running across the description of the man who had bought that particular bit of string and that particular bit of paper .sx Inspector French would have done that , and probably Inspector Wilson ( Margaret and G. D. H. Cole ) also .sx But it is the former group that we are concerned with .sx They are not compelled to undertake vast laborious searches in East London ; they are far above the drudgery of ransacking all the tobacco-shops of Glasgow :sx or questioning the wives of all the sewer-men in Huddersfield .sx They are set down in a compact , isolated country-house community with a corpse and from fifteen to twenty potential murderers , and their job is , like the reader's , to spot the right one .sx It follows , therefore , that our professional detective must be not only shrewd , painstaking and untiring ; he must have a dash of real brilliance in him as well .sx For this country-house stuff is exceedingly tricky work , and the clues are many and distracting .sx He must also be , though this is only a minor detail , of sufficiently good social' standingto wear a tail-coat and dine with the house-party ; otherwise the author will let himself in for a number of small worries about the man's meals .sx And lastly , he must be big and strong .sx Nowadays we all know that he started his career as a uniformed man upon a beat .sx So much then for the detective .sx The actual House-Party is , as we have seen , composed of as many guests as the novelist can find Motives .sx A few years ago , if X=the number of Motives , then the number of guests invariably equalled X+2 .sx For there was a rigid convention that , in order to improve the chance of selling the serial rights , a love-affair was absolutely essential , and it was invariably provided by an amiable , bright , unsophisticated young couple who could not conceivably have killed anyone .sx There was a time , a dreadful time , when it was possible that after the detectives had failed , these two innocent young dears would take it in hand and solve the problem without any difficulty .sx Happily , that possibility is sternly excluded in up-to-date work , for , happily also , the young dears are almost entirely excluded from the book itself .sx Apparently serial rights no longer depend for their value upon a happy love-story to wind up a tale of blood and darkness .sx Would that this ray of sunshine would extend and illuminate the West-End stage as well !sx It is not so very long ago that a play by Mr. A. A. Milne ( it had a successful run ) contained a perfectly appalling brace of sweet young pets who applied themselves to an insoluble mystery and solved it in a twinkling , and , if I remember rightly , arrested the villains , who were a couple of particularly dangerous ruffians from the neighbourhood of Johannesburg , and handed them over to the local gendarmerie .sx The guests themselves must not have individual characters .sx This is ex- .sx tremely important , and I fully realize that the statement requires explanation and , for the sceptical , proof .sx It will receive both .sx Let us go back to fundamentals for a moment and remind ourselves that the essence of this kind of book is that the clever and experienced reader will have a chance of spotting the murderer , and that the rest will be completely and satisfactorily befogged .sx Very well .sx The clues to his identity must be there , but they must be very carefully hidden .sx