It is for Mr. McCarthy to enlist the aid of the Press on occasion. It is sometimes necessary to give wide publicity to a description or a photograph. Then skilful diplomacy is necessary to avoid giving facts which, instead of helping, might hamper an investigation. Only of late years has this co-operation been sought--and credit is due to Mr. Froest for the manner in which he helped to initiate and apply the system. Swift publicity has often helped to run down a criminal, notably in the case of the murderer Crippen. Immediately associated with Mr. McCarthy at headquarters are four Chief Detective-Inspectors--Ward, Fowler, Hawkins, and Gough--all men of long experience and proved qualities. Most of their names are familiar to the public in connection with the unravelling of mysteries during the last decade. One Chief Detective-Inspector--Mr. Wensley--has his headquarters in the East End. One or more of these is always available in an emergency. Is there an epidemic of burglary at some district in London? A chief-inspector is sent to organise a search for the culprits, taking with him a detachment from Scotland Yard to reinforce the divisional detectives. Problems of crime that affect London as a whole are dealt with by them. Some have specialist knowledge of particular classes of crime or particular districts, though each must be competent to undertake any investigation, no matter what it may be. Or a provincial police force may ask for expert aid in, for instance, a baffling murder mystery. One may be sent by the authority of the Home Secretary to assist in its solution. To each of the twenty-two divisions into which the Metropolitan Police is split up are assigned between twelve to thirty detectives, under a divisional inspector. In ten of the larger divisions there is a junior inspector to assist in the control of the staff. Except in a few of the outlying districts there are one, two, three or more detectives to every police station. They deal with local crime, make it their business to know local thieves, and reinforce other divisions or are reinforced as occasion demands. They have special duties allotted to them, and have to keep a record in their diaries of the manner in which their time is spent. Yet individuality and initiative are not sacrificed by too rigid a discipline. If a man learnt, for instance, while watching for pickpockets in the Strand that a robbery was being planned at Kennington, it would be his duty to make at once for the scene. He would stay for nothing, gathering assistance, if possible, as he went, but, if not, going alone. Usually, it is found that the divisional men can deal with any matter needing attention in their districts, but occasionally London is startled by some great mystery. It is then that the C.I.D. moves swiftly, with every nerve strained to achieve its ends.