So far as our purposes are concerned, it began to happen on an afternoon at the end of the month of March of this present year, when J. J. Mullinix, of the Secret Service, called on Miss Mildred Smith, the well-known interior decorator, in her studio apartments on the top floor of one of the best-looking apartment houses in town. For Mullinix there was a short delay downstairs because the doorman, sharp on the lookout to bar pestersome intruders who might annoy the tenants, could not at first make up his mind about Mullinix. In this building there was a rule against solicitors, canvassers, collectors, pedlar men and beggar men; also one against babies, but none against dogs--excepting dogs above a certain specified size, which--without further description--should identify our building as one standing in what is miscalled the exclusive residential belt of Manhattan Island. The doorman could not make up his mind offhand whether Mullinix was to be classified as a well-dressed mendicant or an indifferently dressed book agent; he was pretty sure, though, that the stranger fell somewhere within the general ban touching on dubious persons having dubious intentions. This doubt on the part of the doorman was rather a compliment to Mullinix, considering Mullinix's real calling. For Mullinix resembled neither the detective of fiction nor yet the detective of sober fact, which is exactly what the latter usually is--a most sober fact; sober, indeed, often to the point of a serious and dignified impressiveness. This man, though, did not have the eagle-bird eye with which the detective of fiction so often is favoured. He did not have the low flattened arches--frontal or pedal--which frequently distinguish the bona-fide article, who comes from Headquarters with a badge under his left lapel and a cigar under his right moustache to question the suspected hired girl. About him there was nothing mysterious, nothing portentous, nothing inscrutable. He had a face which favourably would have attracted a person taking orders for enlarging family portraits. He had the accommodating manner of one who is willing to go up when the magician asks for a committee out of the audience to sit on the stage. Not ten individuals alive knew of his connection with the Secret Service. Probably in all his professional life not ten others--outsiders--had ever appraised him for what he was. His finest asset was a gift of Nature--a sort of protective colouration which enabled him to hide in the background of commonplaceness and do his work with an assurance which would not have been possible had he worn an air of assurance. In short and in fine, Mullinix no more resembled the traditional hawkshaw than Miss Mildred Smith resembled the fashionable conception of a fashionable artist. She never gestured with an upturned thumb; nor yet made a spy-glass of her cupped hand through which to gaze upon a painting. She had never worn a smock frock in her life.