A pause, during which the eager light in the young detective’s eye clouded over.  Presently he remarked: 

“How will the finding of another O. B. alter Mr. Brotherson’s position?  He still will be the one person on the spot, known to have cherished a grievance against the victim of this mysterious killing.  To my mind, this discovery of a more favoured rival, brings in an element of motive which may rob our self-reliant friend of some of his complacency.  We may further, rather than destroy, our case against Brotherson by locating a second O.B.”

Mr. Gryce’s eyes twinkled.

“That won’t make your task any more irksome,” he smiled.  “The loop we thus throw out is as likely to catch Brotherson as his rival.  It all depends upon the sort of man we find in this second O. B.; and whether, in some way unknown to us, he gave her cause for the sudden and overwhelming rush of despair which alone supports this general theory of suicide.”

“The prospect grows pleasing.  Where am I to look for my man?”

“Your ticket is bought to Derby, Pennsylvania.  If he is not employed in the great factories there, we do not know where to find him.  We have no other clew.”

“I see.  It’s a short journey I have before me.”

“It’ll bring the colour to your cheeks.”

“Oh, I’m not kicking.”

“You will start to-morrow.”

“Wish it were to-day.”

“And you will first inquire, not for O. B., that’s too indefinite; but for a young girl by the name of Doris Scott.  She holds the clew; or rather she is the clew to this second O. B.”

“Another woman!”

“No, a child;—­well, I won’t say child exactly; she must be sixteen.”

“Doris Scott.”

“She lives in Derby.  Derby is a small place.  You will have no trouble in finding this child.  It was to her Miss Challoner’s last letter was addressed.  The one—­”

“I begin to see.”

“No, you don’t, Sweetwater.  The affair is as blind as your hat; nobody sees.  We’re just feeling along a thread.  O. B.’s letters —­the real O. B., I mean, are the manliest effusions possible.  He’s no more of a milksop than this Brotherson; and unlike your indomitable friend he seems to have some heart.  I only wish he’d given us some facts; they would have been serviceable.  But the letters reveal nothing except that he knew Doris.  He writes in one of them:  ’Doris is learning to embroider.  It’s like a fairy weaving a cobweb!’ Doris isn’t a very common name.  She must be the same little girl to whom Miss Challoner wrote from time to time.”

“Was this letter signed O. B.?”

“Yes; they all are.  The only difference between his letters and Brotherson’s is this:  Brotherson’s retain the date and address; the second O. B.’s do not.”

“How not?  Torn off, do you mean?”

“Yes, or rather, neatly cut away; and as none of the envelopes were kept, the only means by which we can locate the writer is through this girl Doris.”