But the informer is not always called upon to make a public appearance. Many of the tales we read about the marvellous discovery of a clue by the police would be shorn of their romance if we knew that an important fact was being kept in the background--viz. that the detective in charge of the investigation had received a communication informing him exactly where to look for the incriminating piece of evidence. Sometimes the information is anonymous. A few words scribbled on half a sheet of notepaper brought two men to the gallows. The writer suggested that a visit should be paid to a certain house where a little boy would be found who had lost a toy. The hint was taken, and the tale the child told of his missing toy led to one of the most sensational captures of modern times. Nothing was said about the information that furnished the police with the clue. There was no necessity to tell the story, or to produce the anonymous letter. Yet, but for that hint, it is probable that the crime would have remained one of the unfathomed mysteries of the Metropolis. A year or two ago a foreign woman was tried for murder. The evidence--although the body of her victim had been concealed in a trunk--justified a verdict of manslaughter, and the woman only got a term of penal servitude. For two years this woman had been of the greatest assistance to justice. She had become associated with a dangerous class of women in a West End district, and when a man had been robbed by one of them, or by men acting in concert with them, this foreign woman made it her business to find out who the guilty parties were, and to send their names to the police. She was to all intents and purposes a police spy living the life of the class upon whom she was spying, and for certain reasons enjoying their confidence. The professional informer or "nark" is rarely suspected. Personal communication with the authorities is avoided as much as possible. Sometimes, in order to put a desperate gang off the scent, the spy who has been in close relationship with them is arrested too, and discharged on account of "insufficient evidence" to implicate him. To the student of humanity even more interesting than the professional informers are the honest people who become possessed of information with regard to criminal deeds, and from conscientious motives hold their peace. The Roman Catholic clergy never, of course, betray that which they learn under the seal of confession. But it sometimes happens that terrible secrets are learnt by Protestant clergymen, Salvation Army workers, doctors, and nurses. A fierce press discussion raged some years ago around the action of a Salvation Army captain to whom a crime was confessed by a penitent, and who went straight away and gave information. Some people held that the action was justified, others that the confession was made in circumstances which did not justify its betrayal.