As it was necessary to break one of the seals, the object of the robber was to restore it as nearly as possible to its original appearance; and to effect this he used a dampened thimble, rolling it over the wax while the latter was hot. There was but one envelope of the kind in the lot, but it told the whole story to the eye that could penetrate its meaning. As the thimble passed along the edge, it left the mark of the rim, then a smooth, narrow band, followed by pointed elevations closely resembling continuous lines, thus: ======== -------- ........ ........ On the opposite side of the same seal the wax flattened out so as to cover a good deal of surface; and, to give it the desired appearance, the manipulator resorted to the thimble again, but this time USED A DIFFERENT ONE, the indentations on the surface being perceptibly finer and more shallow. The violation of that single seal betrayed the thief, for the detective at once inferred that the job was done in a store where the operator had access to a variety of thimbles. Only one was required; and no person but a merchant would be likely to have more than one within convenient reach. In a store, however, it would be natural to take down a boxful, and place it on the counter, to be selected from at random. One is picked up, used, and thrown back. The operator now finds another spot that requires attention, and without waiting to hunt for the thimble that has already served as a seal,--for the wax is cooling and no time must be lost,--grasps the first that comes to hand, too absorbed in the main issue to give a thought to what would pass as an insignificant subsidiary trifle. No rascal is sharp enough to guard every point,--a general fact that illustrates over and over again, in the experience of man, the seminal truth that in a mercenary and physical as well as in a high and spiritual, sense there is neither wisdom nor profit outside of the limits of absolute integrity and unflinching uprightness. The detective laid aside the papers with a light heart, knowing that at last he was complete master of the situation. Below Camden on the infested route the post-office was kept in a store at two points only, and in one of those no thimbles were sold. The clew pointed unerringly to Raven's Nest as the spot where alone the requisite conditions to account for the imprint on the violated seal were to be found. Thither the officer accordingly went; and the moment his eye rested on Michael Mahoney, Jr., he recognized the heaven-branded features of a thief. Returning to Sioux City, he telegraphed to another agent, who had a large number of the cases growing out of the robberies, to come on at once. The two men took stations, one on each side of Raven's Nest, and in thirty hours they arrested the youthful criminal, who in the interval stole four decoy letters, and paid a portion of the contents to one of the officers who was testing him.