"No question about it being a forgery," that gentleman told him. "You've seen that for yourself. But to suppose that from a mere examination of the writing one can pin it down to a particular person is asking too much. This sort of thing is not an exact science. But I can tell you this. The person who wrote these letters used the same kind of ink as the person who wrote the forged cheque. That ink is chemically different from that used in the genuine cheques. It is a fountain pen ink and I should say that it was used on a broad nib." Which view, taken in conjunction with other matters, carried conviction to Labar, although he knew that he could not formulate a case that would be satisfactory in a court of law. By and by, no doubt, some of the other notes for which the cheque had been changed would come back to the Bank of England, and the chances were that it would be possible to trace them back through the various hands in which they had been. That, however, was likely to be a matter of weeks. What Gertstein's attitude would be in the event of this crime being brought home to his wife had been a matter of speculation with Labar. The little man had insisted on the matter being probed to the bottom, though, of course, he had no suspicion where it would end. The inspector thought it probable that he would refuse to prosecute--perhaps, if his hand was forced, he would declare that there had been no forgery, and that the signature on the cheque was genuine. As matters stood there was no purpose in giving a hint to the millionaire. Labar felt that he would be quite content to ignore the forgery if he could lay Larry Hughes by the heels. He had an idea, not very clearly defined, that he might induce Mrs. Gertstein to clear up many points that troubled him if he could use some weapon to hold over her. Luck favoured him. For the letter that Mrs. Gertstein had written to Larry went to the latter's Hampstead home. Now the Post Office is jealous of the sanctity of the mail--even that of a crook--and there could be no tampering with correspondence under official cognizance. There are more ways of killing a cat than one, however. Some of Labar's men engaged on the task of watching the house had made themselves on good terms with the postmen. And so it was that a delivery bag was left unguarded for two minutes at a certain garden gate. Mrs. Gertstein's letter was included in the next delivery at Larry's house, but meanwhile Labar had become possessed of a copy of it. He whistled a little jig air as he read. Here was a flood of light. Here also--to vary the simile--were muddy waters which it behoved him to stir carefully. Before he made any move it would be well to guard himself. He went to see Marlow, the detective superintendent, who was his immediate chief. Marlow read the letter with impassive face. "Well, Harry? What do you want me to do?"