“I will look farther presently,” said Nick, not inclined to argue the point. “Let me see the Vandyke letter, also the envelope, if you have it.” Mantell took them from a pigeonhole in the desk and placed them in the detective’s hand. Nick turned to the window and began to inspect them with his lens, which he had not replaced in his pocket. He did not read the letter, which covered several closely written sheets, and in which he apparently had no interest aside from the paper on which it was written. “A man handling a tool small enough to pick the lock of a desk is very likely to soil the balls of his thumb and fingers with the metal,” he remarked, after several moments. “There are faint marks and smooches both on this envelope and the backs of several sheets of the paper.” “I did not observe them,” said Mantell, noting the detective’s subtle intonation. “What do you make of them, Carter?” “They look very much like finger prints,” said Nick. “Patsy----” “Yes, chief.” Patsy had foreseen what was coming and was alert on the instant. “Mantell’s car is waiting outside,” said Nick, folding the letter and replacing it in the envelope. “His chauffeur will take you to our office and bring you back here. Examine these smooches with a magnifying glass and see what you make of them. If finger prints, compare them with our collection. Report as quickly as possible.” “Trust me for that, chief,” cried Patsy, hastening from the room. “While we are waiting, Mantell, I will have a look around the outside of the house,” said Nick, rising. “I may find evidence that it has been recently entered, in spite of your burglar alarm. You had better wait here. I can work more quickly alone.” Nick walked out through the hall after the last remark, and ten minutes had passed, when he returned. “Well?” questioned Mantell anxiously. “What have you found?” “Nothing positively showing that the house was entered by night,” Nick replied, resuming his seat. “It may have been accomplished through a second-story window, however, several of which can be quite easily reached. I found, nevertheless, positive evidence of something else.” “Of what?” “That two men quite recently were playing the eavesdropper under your library windows,” said Nick. “There are partly obliterated footprints in the greensward and the flower beds flanking the foundation wall below the windows.” “By Jove, is it possible!” “If they were under only one window, I would feel less confident,” Nick added. “The fact that traces of the same impressions appear under all of the windows convinces me that I am right. They were spying outside ten evenings ago.” “How do you fix the exact day?” Mantell questioned perplexedly. “By the character of the imprints and the condition of the near greensward, to which they frequently stepped,” Nick explained. “We had a hard rain eleven days ago, and have had none since then.” “I remember.”