It was not offensively said; but the conviction it expressed was absolute. Sweet.w.a.ter recognised the tone, as one of truth, and inwardly laid down his arms. He could never like the man; there was too much iron in his fibre; but he had to acknowledge that as a foe he was invulnerable and therefore admirable to one who had the good sense to appreciate him.

"I do not want to believe you." Thus did Brotherson supplement his former sentence. "For if I were to attribute those letters to her, I should have to acknowledge that they were written to another man than myself. And this would be anything but agreeable to me. Now I am going to my room and to my work. You may spend the rest of the evening or the whole night, if you will, listening at that hole. As heretofore, the labour will be all yours, and the indifference mine."

With a satirical play of feature which could hardly be called a smile, he nodded and left the room.

XXI. A CHANGE

"It's all up. I'm beaten on my own ground." Thus confessed Sweet.w.a.ter, in great dejection, to himself. "But I'm going to take advantage of the permission he's just given me and continue the listening act. Just because he told me to and just because he thinks I won't. I'm sure it's no worse than to spend hours of restless tossing in bed, trying to sleep."

But our young detective did neither.

As he was putting his supper dishes away, a messenger boy knocked at his door and handed him a note. It was from Mr. Gryce and ran thus:

"Steal off, if you can, and as soon as you can, and meet me in Twenty-ninth Street. A discovery has been made which alters the whole situation."

XXII. O. B. AGAIN

"What's happened? Something very important. I ought to hope so after this confounded failure."

"Failure? Didn't he read the letters?"

"Yes, he read them. Had to, but--"

"Didn't weaken? Eh?"

"No, he didn't weaken. You can't get water out of a millstone. You may squeeze and squeeze; but it's your fingers which suffer, not it. He thinks we manufactured those letters ourselves on purpose to draw him."

"Humph! I knew we had a reputation for finesse, but I didn't know that it ran that high."

"He denies everything. Said she would never have written such letters to him; even goes so far to declare that if she did write them--(he must be strangely ignorant of her handwriting) they were meant for some other man than himself. All rot, but--" A hitch of the shoulder conveyed Sweet.w.a.ter's disgust. His uniform good nature was strangely disturbed.

But Mr. Gryce's was not. The faint smile with which he smoothed with an easy, circling movement, the already polished top of his ever present cane conveyed a secret complacency which called up a flash of discomfiture to his greatly irritated companion.

"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 Sweet.w.a.ter'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."

Sweet.w.a.ter'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."

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."