In London, because it is the capital of the world, are the mysteries of many lands. London is a city of refuge for the outcasts of the Continent. It is an international Alsatia, where the laws from which the alien inhabitants have fled cease to run. There are quiet cafés and restaurants and clubs hidden away in back streets in which men and women meet and eat, drink, dance, and play cards according to their mood, and plot between whiles the deeds that will be ranked with the master crimes of the age. In the dingy lodging-houses of the side streets of Soho the French murderer and murderess may be leading quiet and simple lives while the Parisian police are searching for them through the length and breadth of France. In the Italian quarter that lies off the Gerkenwell Road the agents of the Mafia frequent the little wine-shops and are in constant communication with the heads of the dreaded society in Italy. Here the vendetta that in this country we associate with Italian melodrama and opera is brought to its tragic fulfilment. The stolid London policeman assists at another "stabbing affray" in Little Italy, and is informed that it arose out of a quarrel in a public-house. But behind that quarrel and the stab or the pistol-shot lies a death-sentence passed months ago in Naples or in Milan, and presently the emissary of vengeance, having accomplished his task, is smuggled out of the country by trusty and tried accomplices, who pay their rent punctually to a London landlord, and draw cheques which are honoured by their London banker. There are romances of the "Mysterious East," strange and weird, working themselves out behind closed doors and curtained windows in the by-ways of Limehouse and Millwall. There, amid Hindu and Mohammedan rites, deeds are done whose story would read like a page from "The Arabian Nights." There are gloomy dens near the river in which solemn Chinamen, with impassive frees, are engaged in a business which would seem incredible to the Englishman if he read it in a volume that described the mysteries of Pekin. There are dealers in spells and charms and philtres, and all the stock-in-trade of the witches, the magicians and the sorcerers, carrying on in the centre of London's rush and roar a prosperous trade, not only with the poor and ignorant, but with the rich and cultured. And among all the mysteries of London, few have a deeper or more tragic meaning than those in which the occult and the supernatural play a part. Not all these mysteries lend themselves to the earnest student who seeks only the truth, who wants to see for himself and to tell a plain unvarnished tale. But many do, and it is these that I shall endeavour to lay before the reader, without sensationalism, without exaggeration, telling a simple story of things as they are.