The debt for which the money was owing appeared to be a somewhat mysterious one. Robert Derrick, a man who dealt in horses, or in anything else by which he could make money, and attended all fairs near and far, lived about two miles from Islip. One day, about a year back, Derrick presented himself at the office of Mr. Paul, and asked that gentleman if he would sue Gervais Preen for a sum of money, forty pounds, which had been long owing to him. What was it owing for, Mr. Paul inquired; but Derrick declined to say. Instead of suing him, the lawyer wrote to request Mr. Preen to call upon him, which Mr. Preen did. He acknowledged that he did owe the debt--forty pounds--but, like Derrick, he evaded the question when asked what he owed it for. Perhaps it was for a horse, or horses, suggested Mr. Paul. No, it was for nothing of that kind, Mr. Preen replied; it was a strictly private debt. An arrangement was come to. To pay the whole at once was not, Mr. Preen said, in his power; but he would pay it by instalments. Ten pounds every six months he would place in Mr. Paul's hands, to be handed to Derrick, whom Mr. Preen refused to see. This arrangement Derrick agreed to. Two instalments had already been paid, and one which seemed to have now miscarried in the post was the third. "Mrs. Sym," began Mr. Preen, when he had dived into the sweet-stuff shop, and confronted the post-mistress behind her counter, "do you recollect, one day last week, my asking you to give me back a letter which I had just posted, addressed to Mr. Paul of Islip, and you refused?" "Yes, sir, I do," answered Mrs. Sym. "I was sorry, but----" "Never mind that. What I want to ask you is this: did you notice that letter when you made up the bag?" "I did, sir. I noticed it particularly in consequence of what had passed. It was sealed with a large red seal." "Just so. Well, Mr. Paul declares that letter has not reached him." "But it must have reached him," rejoined Mrs. Sym, fastening her glittering spectacles upon the speaker's face. "It had Mr. Paul's address upon it in plain writing, and it went away from here in the bag with the rest of the letters." "The letter had a ten-pound note in it." Mrs. Sym paused. "Well, sir, if so, that would not endanger the letter's safety. Who was to know it had? But letters that contain money ought to be registered, Mr. Preen." "You are sure it went away as usual from here--all safe?"