Fate had taken charge of that yellow envelope from the moment it was mailed in Mexico; Chance now laid it on a yellow oak table before a yellow-haired girl; Destiny squinted over her shoulder as she drew the letter from its triply violated envelope and spread it out on the table before her.

A rich, warm flush mounted to her cheeks as she examined the document.  Her chance to distinguish herself had arrived at last.  She divined it instantly.  She did not doubt it.  She was a remarkable girl.

The room remained very still.  The five other cipher experts of the P. I. Service were huddled over their tables, pencil in hand, absorbed in their several ungodly complications and laborious calculations.  But they possessed no Rosetta Stone to aid them in deciphering hieroglyphics; toad-like, they carried the precious stone in their heads, M. D.!

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.