The mysteries of crime and of wrong-doing are common to all cities and to all races. They are part and parcel of the history of civilization. It is not my object in these pages to bring out the sensational features of police romance. My desire is to act as a guide to those who would look beneath the surface of life in the world's great capital, who would wander about its highways and by-ways and see with me that which lies hidden from the casual observer. If I can help my readers to see behind the veil, to peer into the dark recesses, to study out-of-the-way aspects of life as it is lived by thousands of their fellow-citizens, I shall have accomplished a task which has for its object not the gratifying of a morbid curiosity, but the better understanding of things as they are in the great city which is at once the wonder and the admiration of the world. We shall see life in many of its strangest phases, in its best and sometimes, perhaps, in its worst. We shall take our journeys in search of London's mysteries at all hours of the day, and sometimes in the dead of night, when all good people are supposed to be in bed and asleep, but when thousands are out earning an honest living, and hundreds are abroad to earn a dishonest one. "How do all these people get money?" is a question which comes naturally to the lips as one gazes at a great crowd of human atoms jostling and elbowing their way along the busy thoroughfares on a working day. And that question puts in a sentence one of the greatest mysteries of modern London. Alike in the City and in the West there are for ever mixing with the crowd men and women whose means of obtaining a livelihood are mysteries to all but themselves. The tragedies and comedies of life cross each other at every movement of the crowd. The melodrama passes side by side with all that is ordinary and humdrum in the monotony of everyday existence. In the 'buses and the trams and the trains the silent passengers sit side by side, and no man troubles about his neighbour. But the mysteries of modem London are represented in the crowded vehicle and in the packed compartment. The quiet-looking woman sitting opposite you in the omnibus knows the secret that the police have been seeking to discover for months. The man who politely raises his hat because he touches you as he passes from his seat would, if the truth were known, be standing in the dock of the Old Bailey to answer a capital charge. The actors and actresses in London's wild romances and terrible tragedies on shoulders with their fellows every day. I had for months upon my study table the card of a man with the story of whose crime a few months later all England rang. He came to me in the ordinary way about a theatrical matter. He had written a pantomime--I have the book of the words--and he was about to write a comic opera. I chatted with him for a quarter of an hour, bade him good-bye, and forgot all about him until he became the sensation of the day.