“What is there to worry about?” Joe asked. “It’s better than not hearing from him at all.” “But I’m not sure that it’s from him.” “Why?” “Your father has an arrangement with me that he would always put a secret sign beneath his signature any time he had occasion to write to me like this. He was always afraid of people forging his name to letters and notes like this and perhaps getting papers or information that they shouldn’t. So we arranged this sign that he would always put beneath his name.” Frank snatched up the note again. “And there’s no sign here. Just his signature.” “It _may_ be his signature. If it isn’t, it is a very good forgery. And it may have been that he forgot to put in the secret sign, although it isn’t like him to do that.” Mrs. Hardy was plainly worried. “If he didn’t write it, then who did?” asked Joe. “Your father has many enemies. There are relatives of criminals whom he has had arrested and there are criminals who have served their terms and have been released. If there has been foul play the note might be meant to keep us from being suspicious and delay any search.” “Foul play!” exclaimed Frank. “You don’t think something has happened to dad?” he added, his face showing his alarm. “The fact that he didn’t put the secret sign underneath his name makes me anxious. What other object could any one have in sending us a note like that, if not to keep us from starting a search for him?” “Well, whether he wrote that note or not, we _will_ start a search for him,” declared Frank firmly. “He merely said not to worry about him. He didn’t order us not to look for him. If he really did write the note he can’t say we were disobeying instructions. And then, the absence of the secret sign makes it all different.” “I’ll say we’ll look for him!” cried Joe. “Vacation starts next week, and we’ll have plenty of time to hunt for him.” “Wait until then, at any rate,” Mrs. Hardy advised. “Perhaps he will return in the meanwhile.” But as she glanced at the note again and once more regarded the signature, strangely lacking its secret sign, her forebodings that Fenton Hardy had met with foul play increased. CHAPTER X THE VAIN SEARCH Fenton Hardy was still missing when the summer vacation began. There had been no word from him. Never, in all his years of detective work, had he vanished from home so completely and for such a length of time. He was an intensely considerate man and his first thought was always for his wife and boys. Occasionally it was necessary for him to leave home suddenly on trips that would keep him away for some length of time, sometimes it seemed wiser to keep the knowledge of his whereabouts to himself. But he always managed to communicate with Mrs. Hardy to assure her of his safety.