Then he smiled grimly, as it occurred to him that the only person from whom, in Dallas’ behalf, such knowledge should have been kept was himself. Of what use to request the landlady not to mention the matter to anybody, when he, the inspector in charge of the case, was already in possession of the incriminating information? He was the man who must find out what had become of the missing pink envelope. He was the man who must name the guilty person, and eventually make an arrest in the case. And, now that he knew that Dallas Worthington had suddenly vanished, a few minutes after she got possession of the only pink envelope which the letter box contained, what was he going to do about it? He asked himself this question uneasily as he walked away from the boarding place. He told himself indignantly that it was preposterous to suppose for a minute that Dallas could be guilty of stealing the missing letter; that she could deliberately have deceived Carrier Andrews in order to get possession of the hundred-dollar bill which the pink envelope contained. He was angry with himself for even considering the possibility of Dallas’ guilt. "A nice way to treat the girl I love--the girl I am going to make my wife!" he muttered. "It would serve me right if she threw me over entirely when she learns that I dared to doubt her. How foolish to suppose that her disappearance can have anything to do with the loss of that letter!" Yet he knew very well that it was not foolish, from the standpoint of an impartial post-office inspector. He knew very well that, considering all the facts in the case, if it had been any other girl than Dallas Worthington, he would have decided with positiveness that the person to be charged with the crime was the young woman who had accosted Pop Andrews at the street letter box, and pleaded with the old mail collector until he handed her the letter. He realized that he must do one of two things: He must scoff at Pop Andrews’ story, accuse him of having invented that yarn about handing the pink envelope to Dallas, charge the veteran carrier with being the thief, and place him under arrest; or else, accepting the carrier’s story as the truth, he must report to his chief that the missing letter had been stolen by a young woman named Dallas Worthington, who had not yet been placed under arrest because she had fled to escape the consequences of her act. "It’s a ticklish proposition," reflected Owen. "I can’t very well accuse Dallas, yet I know very well that Pop Andrews is honest, and it would break the old fellow’s heart to accuse him of being a thief." CHAPTER XVII. UNWELCOME DUTIES. As Sheridan entered the post office, and stepped moodily into the private rooms of the superintendent, Henderson looked at him with an expectant smile. "Well, Mr. Inspector, have you solved the mystery yet?" "Not quite, Henderson. Is Pop Andrews in? I’d like to have another talk with him."