For some time Malcolm Sage was greatly puzzled by the fact that even when the name of a long thoroughfare were indicated in one of the telephone messages, such as Oxford Street, Marylebone Road, or even the Fulham Road, Mr. Naylor never experienced any difficulty in locating the whereabouts of his subordinate. Sage gave instructions for the exact position of each thoroughfare to be indicated. As a result he discovered that contact was always established in the neighbourhood of the building numbered 10. "It's the German mind," remarked Sage one day to Colonel Walton. "It leaves nothing to chance, or to the intelligence of the other fellow." As each one of Mr. Naylor's associates was located, he or she was continuously shadowed. In consequence the strain upon the resources of Department Z. became increasingly severe. It was like an army advancing into an enemy country, and having to furnish the lines of communication from its striking force. Sometimes Sage himself was engaged in the shadowing, and once or twice even Colonel Walton. "By the time we've finished, there won't be even the office cat left," Thompson one day remarked to Gladys Norman, a typist whom Malcolm Sage had picked out of one of the Departments through which he had passed during his non-stop career. She had already shown marked ability by her cleverness and resource, to say nothing of her impudence. "Never mind, Tommy," she had replied. "It's all experience, and after the war, when I marry you and we start our private inquiry bureau----" She nodded her head knowingly. "Why, I've got enough facts from my own department to divorce half the officers on the staff," she added. The work of shadowing Mr. Naylor was not without its humours. Sometimes Department Z. was led away on false scents. On one occasion a week was spent in tracking a venerable-looking old gentleman, he turned out to be a quite respectable pensioned civil servant, who, out of the kindness of his own heart, had passed the time of day with Mr. Naylor. The plan decided upon by Colonel Walton and Malcolm Sage was carefully to watch all Mr. Naylor's associates and, at a given time, make a clean sweep of the lot. To achieve this effect a zero hour was to be established on a certain day. Each was to be arrested as soon after that time as it was possible. This was mainly due to Malcolm Sage's suspicion that some scheme of warning existed between the various members of the combination, whereby any danger threatening one was quickly notified to all the others. "In all probability we shall get a few harmless birds into the net," Malcolm Sage had remarked. "Probably the sister of an M.P., or the head of a department in one of the new Ministries; but that can't be helped." "Still I should prefer that it didn't happen," Colonel Walton had said drily. "You know the Skipper hates questions in the House."