It is not unreasonable to give a rough synopsis and follow Julian Symons. That is what happens here.

There are stories of natural cunning going back to the Bible, and there are famous early examples like Voltaire's Zadig featuring the deductions relating to descriptions of a missing horse and dog which Umberto Eco pastiches in The Name Of The Rose. Then in another line there are criminal tales passing through Defoe's Moll Flanders, Fielding's Jonathan Wilde and the anonymous Newgate Calendars. There has obviously always been a mass interest in crime, (who would believe that anyone in the past enjoyed being a victim anymore than someone today might do), but there was almost no interest in those who caught criminals. Now criminals and thieftakers may have been close but there must have been some effective workers in the field, such as the blind magistrate Sir John Fielding who founded the Bow Street Runners, and some honest Runners. Yet there are few accounts of their work and methods (though there were some written, of which modern pastiches give a poor impression).

In the nineteenth century these began to mutate again into the three decker novels of the period by Harrison Ainsworth, Bulwer Lytton, and of course Dickens, Trollope and Collins. Early Dickens shows this tradition clearly (think of the distinction between Oliver Twist in Fagin's den, obvious to the reader, with Dickens' later treatment of David Copperfield and Uriah Heep's fraud in Mr Wickfield's office). These writers were often called the Sensation Novelists, because that is what they aimed at in their melodramas. On much lower level there were the Penny Dreadfuls.

Now from abroad came two sources: firstly from France came the memoirs of Vidocq - a criminal who reformed and became head of the Surete. Those memoirs read like a novel (and were ghostwritten, and possibly fictionalised) but were read keenly in English translations. Vidocq described going about in disguise, his searches of lodgings, trailing endlessly about boarding houses checking papers and comparing signatures, and finally revealing himself to his victim with the words 'I am Vidocq'; all this combining routine with exoticism and success.

One of his readers was an American with a taste for the exotic in other elements of his personal life, but also in his reading and his writing. Amid these tales of the grotesque and arabesque, though, there are five stories that stand out. He was Edgar Allen Poe, and his five stories were 'The Murders in the Rue Morgue', 'The Purloined Letter', 'The Murder of Marie Roget', 'The Gold Bug' and 'Thou Art the Man'. The first three of these feature the detective Chevalier C. Auguste Dupin, where Dupin uses his mind to solve the apparantly impossible crimes - the first a murder in a locked and inaccessible room, the second the discovery of a missing letter hidden where it was most obvious, and the third the solution of a real-life crime. 'The Gold Bug' revolved around crypto-analysis, something on which Poe also wrote non-fiction. And all of them introduce the two ideas of the supremacy of reason, and the idiosyncracies of the detective who is capable of reason, and the invisibility of it to those about him. Thus, the American Poe was the second foreign influence on the development of the classic detective story.

The Metropolitan Police were created in 1829, but the Bow Street Runners were not wound up until ten years later, when they were replaced by a Detective Department with a staff of eight. Very quickly identification with a romantic criminal hero was transferred to a romantic detective in literature.

In 1860 Wilkie Collins published The Woman In White, a thriller that became an immediate and sensational bestseller, and then, in 1868, The Moonstone, the first detective novel. Now, Dickens knew Poe and his work, but whether Collins did so is less certain. So possibly with very little awareness of what authors had done before him Collins gave his readers a mystery which they might solve, and a detective who did solve it, the professional Sergeant Cuff (who was based on the real Jonathan Whicher, a colleague of the Inspector Field whom Dickens admired, and accompanied on patrol) and a new kind of work.

There were other novels and stories about crime from authors of all countries - French such as Gaboriau's, Scots such as R.L. Stevenson's, Americans such as Mark Twain (whose Pudd'nhead Wilson revolves around fingerprints). Still these had not had an influence in creating a genre. In 1886 Doyle who liked these sorts of things (but wanted to write, and did write, historical novels) wrote A Study In Scarlet and in 1889 his second Holmes story, another novel The Sign of the Four. Both of these are broken in structure - each a long story about Holmes followed by another story giving the background. Two years later Doyle defined his medium much more clearly - a series of complete stories maintaining the central characters, a continuity which had been missing from The Strand until 'A Scandal In Bohemia' appeared in July 1891 and 'The Red-headed League' a month later used the same characters again.

Now there must have been a social background, too. The capital for The Strand magazine came from the profits of Tit-Bits, written to entertain people who had been taught to read at board school, but did not want or could not cope with anything of greater difficulty. Wilkie Collins had recognised that this public ('The Unknown Public', he called it in 1858) existed - he reached it by republishing his books in cheap editions - but it clearly took decades for them to be satisfied, if the sales-figures for The Strand are to be trusted. The other interest must be that there had been enough growth in economic advantage that people though they had something to protect - that the police were there to protect you, rather than restrain you. And, of course, you knew that this all revolved around the age of technical marvels and had some understanding of how reason was applied to all this.

Two good overviews are Julian Symons's Bloody Murder, now in its third edition, and Leroy Ladd Panek's An Introduction to the Detective Story.