Then there was dead silence. Again he hammered at the door. A slight snap suddenly sounded. This was caused by the cover to the little circular hole in being shot back. “What do you want?” sharply demanded the voice of some one behind the hole, invisible for the darkness of the closed in room or entry beyond. “Is this the United States Mail Order House?” asked Frank. “The what?” Frank repeated the magnificent-sounding name. “Never heard of it.” “Well, then, is there a Mr. Wacker here?” persisted Frank. “No. Nobody but a sick old man. Go away.” “Hold on,” said Frank, but the wicket went shut with a sudden snap. “Of course this is the place,” thought Frank. “That’s something to know. Hello--” Five steps down the stairs Frank started. Something had struck his shoulder. As he turned he noticed the window being pulled to. Also at his feet the object that had struck him. It was a little piece of tin--around it was tied a fragment of coarse manilla paper. Frank picked it up. He slipped it into his pocket and descended to the street. Turning the corner he untied the paper. It was scrawled over, and read: “Keep cool. Be shady. Things working. Important. Midnight.” Frank had to smile at all this serio-tragic phraseology. “Stet wrote that,” he said. “Still the dark and mysterious detective! Probably enjoying it. He usually means something though, for all his extravagant ways of mystery. That means he has news to tell me. But where does he expect to see me at midnight? And why midnight? “Ah! Brr-rr-r! Hist! Good old Stet! He’ll probably do something sensational soon, but meantime I must pursue my investigations.” These did not result in much. Frank went to the post-office. The postmaster told him that twice a day either Dale Wacker or an old man who was evidently associated with him brought a great many letters to mail. In return they received as many as forty letters a day. They presented a good many money orders, always for the same amount--eleven dollars. The afternoon was nearly gone by this time. Frank called at the town hall but found that the marshal had gone home to sleep until midnight. “I will see him bright and early in the morning,” decided Frank. “He can’t make any mistake by assuming that old lodge room to be the headquarters of the United States Mail Order House Swindle. Those fellows are taking some risks. They will be in for a sudden disappearance unless the marshal nabs them soon.” “Are you going to take a day or two looking up Markham?” his mother asked at the tea table. “I can’t to-morrow, mother,” continued Frank--“other important business. I hope to get the day following, though.” Frank put in an hour on a small set of books he kept at home covering the mail order business. Then he went to bed. Something disturbed him about two hours later, for, almost wide awake, he counted the strokes of the town bell. It was just twelve o’clock.