“F.” CHAPTER XV A DOCUMENT OF IMPORTANCE It was a copy, and not the original, of this pitiful letter which I found in the cigar-case, as was evident from the fact that the document was in Green’s handwriting, and to this I attached some importance. As matters stood it _looked_ as if Green had in some way contrived to intercept Mullen’s correspondence; and it also looked as if, after making himself acquainted with the contents of Mullen’s letters, Green had carefully resealed them and let them go on to the person for whom they were intended. That he must have had some reason for not retaining in his possession what might prove so valuable a piece of evidence was very clear, and after thinking the matter over I came to the following conclusion. Although Mullen had given an address to which a letter might be sent to him by his sister, it was not likely that he himself was actually to be found at that address. On the contrary, it was more than probable that he had arranged some complicated and roundabout system of reforwarding correspondence, so that even if the police should find out the address to which the letter was sent, they would still have before them the difficult task of tracing the letter to the address to which it had been reforwarded, and perhaps again reforwarded, before they could come to the actual hiding-place of the fugitive, who in the meantime would get wind of what was going on and would promptly decide that it was high time for him to change his quarters. And I felt tolerably sure that his manner of making a change would be like that of certain sea-fowl who, upon the approach of an enemy, dive out of sight beneath the water, where they twist and turn and eventually come up far out of reach and range, and in any other direction than that in which they are looked for.