“He says that, does he?  You found him on the whole tolerably straightforward, eh?  A hard nut; but hard nuts are usually sound ones.  Come, now! prejudice aside, what’s your honest opinion of the man you’ve had under your eye and ear for three solid weeks?  Hasn’t there been the best of reasons for your failure?  Speak up, my boy.  Squarely, now.”

“I can’t.  I hate the fellow.  I hate any one who makes me look ridiculous.  He—­well, well, if you’ll have it, sir, I will say this much.  If it weren’t for that blasted coincidence of the two deaths equally mysterious, equally under his eye, I’d stake my life on his honesty.  But that coincidence stumps me and—­and a sort of feeling I have here.”

It is to be hoped that the slap he gave his breast, at this point, carried off some of his superfluous emotion.  “You can’t account for a feeling, Mr. Gryce.  The man has no heart.  He’s as hard as rocks.”

“A not uncommon lack where the head plays so big a part.  We can’t hang him on any such argument as that.  You’ve found no evidence against him?”

“N—­no.”  The hesitating admission was only a proof of Sweetwater’s obstinacy.

“Then listen to this.  The test with the letters failed, because what he said about them was true.  They were not meant for him.  Miss Challoner had another lover.”

“Only another?  I thought there were a half-dozen, at least.”

“Another whom she favoured.  The letters found in her possession —­not the ones she wrote herself, but those which were written to her over the signature O. B. were not all from the same hand.  Experts have been busy with them for a week, and their reports are unanimous.  The O. B. who wrote the threatening lines acknowledged to by Orlando Brotherson, was not the O. B. who penned all of those love letters.  The similarity in the writing misled us at first, but once the doubt was raised by Mr. Challoner’s discovery of an allusion in one of them which pointed to another writer than Mr. Brotherson, and experts had no difficulty in reaching the decision I have mentioned.”

“Two O. B.s!  Isn’t that incredible, Mr. Gryce?”

“Yes, it is incredible; but the incredible is not the impossible.  The man you’ve been shadowing denies that these expressive effusions of Miss Challoner were meant for him.  Let us see, then, if we can find the man they were meant for.”

“The second O. B.?”

“Yes.”

Sweetwater’s face instantly lit up.

“Do you mean that I—­after my egregious failure—­am not to be kept on the dunce’s seat?  That you will give me this new job?”

“Yes.  We don’t know of a better man.  It isn’t your fault, you said it yourself, that water couldn’t be squeezed out of a millstone.”

“The Superintendent—­how does he feel about it?”

“He was the first one to mention you.”

“And the Inspector?”

“Is glad to see us on a new tack.”