He murdered and robbed a fellow-traveller in a railway carriage, made his escape, and was found hiding in a back street London lodging, brought to justice, convicted and executed. One of the most famous adventuresses of our day, a woman whose whole life had been a romance of daring imposture, left her umbrella in my hall-stand when she drove away in a hansom. She came to claim it a week later. In the meantime she had committed a fraud which later on secured her a long term of penal servitude. It never for a moment in these cases crossed my mind that I was entertaining a man capable of a brutal murder and a woman who was to rank among the celebrated female impostors of the century. To few of us does it occur as we come and go in the course of the day's work or pleasure that we are actually in touch with the mysteries of wickedness and crime. Going from the Old Bailey not long since, at the conclusion of a murder trial, I got to Farringdon Street just as a train was starting, and scrambled into a third-class carriage. It was nearly full, and I took the last seat. Instantly I recognized two of my fellow-travellers. They were an elderly woman and a young woman, both dressed in deep black. No one took any notice of them. But what objects of interest they would have been to the other passengers had the identity of one of them been known! She was the affianced wife of a young man who had that day been condemned to death for the barbarous murder of the woman to whom he was already married. The girl who was sitting with her mother in the crowded compartment on the Metropolitan Railway had just parted with the man who had murdered another woman to make her his wife, and had that day been sent to the gallows. I had heard this poor girl on the previous day tell in the crowded court one of the strangest incidents of the tragedy. When all London was ringing with the mystery of the murder, her affianced husband came to tea with her people. The talk turned upon the startling crime, and everybody present said they hoped the murderer would soon be discovered. And all the time the murderer was sitting at the tea-table, the honoured guest of that happy little family party! It is because its mystery has fascinated me from the beginning, and because the spell has never been weakened, that I have wandered London in every direction night and day in a ceaseless endeavour to know it in every phase and form. In these years of wandering, often far off the beaten track, I have learnt much that is not common knowledge, and every day I am learning more. If I were to say that London has laid its heart bare to me it would be untrue, for that has happened to no man. Many of its inner workings are mysteries even to those whose task in life it is to solve them. But I have penetrated far enough to be able to act as guide to those who have no opportunity of making the journey by themselves, who, even if they had, would make it with small profit to their knowledge of facts.