As he listened for a moment longer, and then stooped to gather up the debris which had fallen on his own side of the partition, he muttered, in his old self-congratulatory way: 

“If the devil don’t interfere in some way best known to himself, this opportunity I have made for myself of listening to this arrogant fellow’s very heartbeats should give me some clew to his secret.  As soon as I can stand it, I’ll spend my evenings at this hole.”

But it was days before he could trust himself so far.  Meanwhile their acquaintance ripened, though with no very satisfactory results.  The detective found himself led into telling stories of his early home-life to keep pace with the man who always had something of moment and solid interest to impart.  This was undesirable, for instead of calling out a corresponding confidence from Brotherson, it only seemed to make his conversation more coldly impersonal.

In consequence, Sweetwater suddenly found himself quite well and one evening, when he was sure that his neighbour was at home, he slid softly into his closet and laid his ear to the opening he had made there.  The result was unexpected.  Mr. Brotherson was pacing the floor, and talking softly to himself.

At first, the cadence and full music of the tones conveyed nothing to our far from literary detective.  The victim of his secret machinations was expressing himself in words, words;—­that was the point which counted with him.  But as he listened longer and gradually took in the sense of these words, his heart went down lower and lower till it reached his boots.  His inscrutable and ever disappointing neighbour was not indulging in self-communings of any kind.  He was reciting poetry, and what was worse, poetry which he only half remembered and was trying to recall;—­an incredible occupation for a man weighted with a criminal secret.

Sweetwater was disgusted, and was withdrawing in high indignation from his vantage-point when something occurred of a startling enough nature to hold him where he was in almost breathless expectation.

The hole which in the darkness of the closet was always faintly visible, even when the light was not very strong in the adjoining room, had suddenly become a bright and shining loop-hole, with a suggestion of movement in the space beyond.  The book which had hid this hole on Brotherson’s side had been taken down—­the one book in all those hundreds whose removal threatened Sweetwater’s schemes, if not himself.

For an instant the thwarted detective listened for the angry shout or the smothered oath which would naturally follow the discovery by Brotherson of this attempted interference with his privacy.

But all was still on his side of the wall.  A rustling of leaves could be heard, as the inventor searched for the poem he wanted, but nothing more.  In withdrawing the book, he had failed to notice the hole in the plaster back of it.  But he could hardly fail to see it when he came to put the book back.  Meantime, suspense for Sweetwater.