At that moment Frank and Joe came into the house, flushed from their outing on the bay. They were laughing at the recollection of some remarkable acrobatic feats that Chet Morton had attempted on the bow of the motorboat, the result of which had been the sudden immersion of Chet in the chilly waters of the bay. He had just left them, his clothes dripping wet, heading for home on his motorcycle, vowing that he could have stood on his hands on the bow of the boat if only Frank hadn't steered to the left when he should have steered to the right. "However," he had said cheerfully, "I missed my bath last Saturday night, anyway, so this will make up for it." The Hardy boys recounted their adventures and after Fenton Hardy had chuckled over the plight of Chet he tossed over the mysterious letter to them. "What do you think of that?" he asked of the boys. Frank and Joe read the scrawled warning with interest. "Trying to frighten you away from the case, are they?" said Frank, as he gave back the note. "Looks like it." "You won't pay any attention to it, of course?" "Not a bit. Although your mother seems to think I'll be carried home on a stretcher any day." "When did the note come?" Joe inquired with deep interest. Mrs. Hardy told them how the strange letter had been delivered, and when they learned that it had been left at the door instead of being sent through the post-office both boys became immediately excited. They did not, however, air their suspicions at the time and it was not until they were alone after supper that they discussed the topic between them. "That settles it!" declared Frank with finality. "The counterfeiters _must_ be right here in Bayport." "Or near by." "That's what I mean. If they were out of town, the letter would have been sent by mail." "It's getting to be a little too much. As dad said, it was adding insult to injury--tricking mother to the extent of eight hundred dollars and now sending an impudent note like that. It's up to us to use what we know." "You mean to see if we can find out anything more about the mill?" "I mean to find out everything there is to be found out about it." "I'm with you. When do we start?" "When should we?" "To-night." "So soon?" "Why not?" "It's all right with me." "If we're going to go back there at all we may as well get it over with as soon as we can," said Frank. "I've been thinking over a way to get away with it and I think we should be able to get inside that place and investigate it without much trouble." "How?" "Do you remember how Carl Stummer remarked that you looked something like Lester?" "Yes." "And there is a bit of a resemblance, too. You are of about the same build, and you both have fair, curly hair. I think you should be able to impersonate him if we went around there at night. At a distance, and at night time, they might mistake you for him, even if we were discovered."