However it may originate, there is still little doubt of the universality, the perennial activity of crime. We may accept the unpleasant fact without theorising further as to the genesis of crime. I propose in these pages to take criminals as I find them; to accept crime as an actual fact, and in its multiform manifestations; to deal with its commission, the motives that have caused it, the methods by which it has been perpetrated, the steps taken--sometimes extraordinarily ingenious and astute, sometimes foolishly forgetful and ineffective--to conceal the deed and throw the pursuers off the scent; on the other hand, I shall set forth in some detail the agencies employed for detection and exposure. The subject is comprehensive, the amount of material available is colossal, almost overwhelming. Every country, civilised and uncivilised, the whole world at large in all ages, has been cursed with crime. To deal with but a fractional part of the evil deeds that have disgraced humanity would fill endless volumes; where "envy, hatred, and malice, and all uncharitableness" have so often impelled those of weak moral sense to yield to their criminal instincts, a full catalogue would be impossible. It must be remembered that crime is ever active in seeking new outlets, always keen to adopt new methods of execution; the ingenuity of criminals is infinite, their patient inventiveness is only equalled by their reckless audacity. They will take life without a moment's hesitation, and often for a miserably small gain; will prepare great coups a year or more in advance and wait still longer for the propitious moment to strike home; will employ address and great brain power, show fine resource in organisation, the faculty of leadership, and readiness to obey; will utilise much technical skill; will assume strange disguises and play many different parts, all in the prosecution of their nefarious schemes or in escaping penalties after the deed is done. With material so abundant, so varied and complicated, it will be necessary to use some discretion, to follow certain clearly defined lines of choice. I propose in these pages to adopt the principle embodied in the title and to deal more particularly with the "mysteries" of crime and its incomplete, partial, or complete detection; with offences not immediately brought home to their perpetrators; offences prepared in secret, committed by offenders who have long remained perhaps entirely unknown, but who have sometimes met with their true deserts; offences that have in consequence exercised the ingenuity of pursuers, showing the highest development of the game of hide-and-seek, where the hunt is man, where one side fights for life and liberty, immunity from well-merited reprisals, the other is armed with authority to capture the human beast of prey. The flights and vicissitudes of criminals with the police at their heels make up a chronicle of moving, hair-breadth adventure unsurpassed by books of travel and sport.