It was at a Delmonico ball, which was given in honor of a person of royal descent, and on the Friday evening preceding Ray Palmer's visit to Hazeldean, that Mr. Rider found his plans ripe for action and accomplished his great _coup de grâce_. He had learned, through the pretty servant-girl, that Mrs. Vanderheck was to grace the occasion with her presence and was to be attired in a costume of unusual richness and elegance--"with diamonds enough to blind you," the lively and voluble Fanny had boasted to her admirer. Consequently the detective got himself up in elaborate style, obtained a ticket for the ball by some means best known to himself, and, when the festivities were at their height, slipped in upon the brilliant scene. He was not long in "spotting" his prey, who was conspicuous in white brocaded velvet and white ostrich tips, while her person was literally ablaze with diamonds. "Great Scott!" the man muttered, as he ran his keen eye over her gorgeous attire; "it is a mystery to me how any woman dare wear such a fortune upon her person; she is liable to be murdered any day. Why, she--Aha!" His heart gave a sudden leap, and for a moment, as he afterward described his sensations, it seemed as if some one had struck him on the head with a club, for he actually saw stars and grew so dizzy and confused that he could scarcely stand; for--_in the woman's ears he caught sight of a gleaming pair of crescents_! He soon recovered himself, however, and took a second look. He had, as we know, been looking for those peculiar ornaments for more than three years, and now he had found them, as he had always believed he should, upon a gay woman of fashion in the midst of fashionable admirers. It did not take him long to decide upon his course of action, and he was now again the cool and collected detective, although the fierce glitter in his eyes betrayed some relentless purpose in his mind. He made his way quietly into a corner, where he stood covertly watching the brilliant woman, and comparing her appearance with a description that was written in cipher upon some tablets which he took from his pocket.