‘I’m going to ask you, monsieur,’ he said, when he had drawn that gentleman aside, ‘to do me a rather unusual favour. I have just bought this machine, and I want you to see it before I take it away, and, if you will be so kind, to give me some information about it. I shall tell you in confidence why I ask. I am a detective, employed on behalf of a man charged with a serious crime, but who I believe is innocent. A certain letter, on the authorship of which his guilt largely depends, was written, if I am not mistaken, on this machine. You will forgive me if I do not go into all the particulars. An adequate identification of the typewriter is obviously essential. I would therefore ask you if you would be kind enough to put a private mark on it. Also, if you would tell me how it came into your possession, I should be more than obliged.’ ‘I shall do what you ask with pleasure, monsieur,’ returned the manager, ‘but I trust I shall not be required to give evidence.’ ‘I do not think so, monsieur. I feel sure the identity of the machine will not be questioned. I make my request simply as a matter of precaution.’ The manager, with a small centre punch, put a few ‘spots’ on the main frame, noting the machine’s number at the same time. ‘Now you want to know where we got it,’ he went on to La Touche. ‘Excuse me a moment.’ He disappeared to his office, returning in a few minutes with a slip of paper in his hand. ‘The machine was received from the Avrotte Pump Construction office’--he referred to the paper--‘on 2nd April last. It was supplied to the firm several years earlier, and on the date mentioned they exchanged it for a more up-to-date machine, a No. 10.’ ‘I am extremely obliged, monsieur. You may trust me to keep you out of the business if at all possible.’ Calling a taxi, La Touche took the machine to his hotel in the rue de La Fayette. There he typed another sample, and, using a powerful lens, compared the letters with the photographic enlargements he had obtained of the Le Gautier type. He was satisfied. The machine before him was that for which he had been in search. He was delighted at his success. The more he thought of it, the more certain he felt that Boirac’s fault-finding was merely an excuse to get rid of the typewriter. And the manufacturer had dismissed Mlle. Lambert simply because she knew too much. If inquiries were made in the office, he would be safer with her out of the way. And as to Boirac’s deeper object. So far as the detective could see, there could be only one explanation. Boirac knew the Le Gautier letter was done on that machine. And if he knew, did it not follow that he had sent the letter to Felix? And if he had sent the letter, must he not be guilty? To La Touche it began to look like it.