No indiscreet sound interrupted their mental gymnastics, save only the stealthy scrape of a pen, the subdued rustle of writing paper, the flutter of a code-book's leaves thumbed furtively. The yellow-haired girl presently rose from her chair, carrying in her hand the yellow letter and its yellow envelope with yellow slips attached; and this harmonious combination of colour passed noiselessly into a smaller adjoining office, where a solemn young man sat biting an unlighted cigar and gazing with preternatural sagacity at nothing at all. Possibly his pretty affianced was the object of his deep revery--he had her photograph in his desk--perhaps official cogitation as D. C. of the E. C. D.--if you understand what I mean?--may have been responsible for his owlish abstraction. Because he did not notice the advent of the yellow haired girl until she said in her soft, attractive voice: "May I interrupt you a moment, Mr. Vaux?" Then he glanced up. "Surely, surely," he said. "Hum--hum!--please be seated, Miss Erith! Hum! Surely!" She laid the sheets of the letter and the yellow envelope upon the desk before him and seated herself in a chair at his elbow. She was VERY pretty. But engaged men never notice such details. "I'm afraid we are in trouble," she remarked. He read placidly the various memoranda written on the yellow slips of paper, scrutinised! the cancelled stamps, postmarks, superscription. But when his gaze fell upon the body of the letter his complacent expression altered to one of disgust! "What's this, Miss Erith?" "Code-cipher, I'm afraid." "The deuce!" Miss Erith smiled. She was one of those girls who always look as though they had not been long out of a bathtub. She had hazel eyes, a winsome smile, and hair like warm gold. Her figure was youthfully straight and supple--But that would not interest an engaged man. The D. C. glanced at her inquiringly. "Surely, surely," he muttered, "hum--hum!--" and tried to fix his mind on the letter. In fact, she was one of those girls who unintentionally and innocently render masculine minds uneasy through some delicate, indefinable attraction which defies analysis. "Surely," murmured the D. C., "surely! Hum--hum!" A subtle freshness like the breath of spring in a young orchard seemed to linger about her. She was exquisitely fashioned to trouble men, but she didn't wish to do such a-- Vaux, who was in love with another girl, took another uneasy look at her, sideways, then picked up his unlighted cigar and browsed upon it. "Yes," he said nervously, "this is one of those accursed code-ciphers. They always route them through to me. Why don't they notify the five--" "Are you going to turn THIS over to the Postal Inspection Service?" "What do you think about it, Miss Erith? You see it's one of those hopeless arbitrary ciphers for which there is no earthly solution except by discovering and securing the code book and working it out that way."7 She said calmly, but with heightened colour: