“Your pleasure could not be greater than mine, Mr. Carter. I am delighted to see you. I ought to scold you roundly, however, for not having called here occasionally, at least.” “That’s right, too, Helen,” put in Mantell. “You overlook one fact,” smiled Nick, replying to her. “What is that, Mr. Carter?” “That I have hardly an hour in the week, not to say in a day, that I can really call my own,” Nick said gravely. “I am a very busy man, you know.” “Ah, I suppose so,” Helen rejoined. “And chiefly because other men are so wicked.” “True.” “It is deplorable.” “True again,” said Nick. “Nor am I less busy than usual this morning. I think, Frank, we had better get right at this matter.” “I think so, too.” “I’m sure your wife will excuse us.” She bowed and smiled agreeably, and Nick and Patsy followed Mantell into the library, a superbly furnished room overlooking the side grounds. “Now, Nick, what can I tell you?” he asked, placing chairs for them. “Why have you come here?” “To begin with, Mantell, I want to see the letter written to you by Calvin Vandyke,” said Nick. “Where have you kept it?” “Here, in my desk,” said Mantell, rising to unlock a large roll-top desk in one corner of the spacious room. “Is your desk usually locked?” “Always, Nick, when I am absent.” “Wait one moment,” said the detective. “Let me examine the lock.” Mantell complied, handing him the key. Nick unlocked the desk, and, rolling the top partly up, he began a careful inspection of the brass socket which received the bolt of the lock when the desk was securely closed. He found several tiny, faint scratches on one side of it, which could not have been caused by the action of the bolt, not being where it came in contact with the socket. An examination with a powerful lens, moreover, showed that these slight marks were quite bright, as if recently made and with an instrument as sharp as the point of a pin. Nick returned the ring of keys and resumed his seat. “That lock has recently been picked, Mantell,” he said confidently. “Picked!” Mantell exclaimed amazedly. “Are you sure of it?” “Positively.” “But----” “There aren’t any buts,” Nick interrupted. “I know when evidence shows that a lock has been picked. The crook who picked that one used a tool with a sharp point, which at times touched one side of the bolt socket and left faint marks in the brass. The brightness of them shows that it was quite recently done.” “But our servants are entirely trustworthy, Nick, and----” “I don’t think it was done by one of your servants,” Nick again interrupted. “Have you a burglar alarm in the house?” “Yes, an electric alarm,” said Mantell. “All of the doors and windows on the ground floor are protected. Perkins, the butler, sets it each night before he retires.” “This job may have been done during the day.” “But there is always some one in the house.”