But the evening was young.  Retrospect comes with later and more lonely hours.  There will be opportunities yet for studying this impassive countenance under much more telling and productive circumstances than these.  He would await these opportunities with cheerful anticipation.  Meanwhile, he would keep up the routine watch he had planned for this night.  Something might yet occur.  At all events he would have exhausted the situation from this standpoint.

And so it came to pass that at an hour when all the other hard-working people in the building were asleep, or at least striving to sleep, these two men still sat at their work, one in the light, the other in the darkness, facing each other, consciously to the one, unconsciously to the other, across the hollow well of the now silent court.  Eleven o’clock!  Twelve!  No change on Brotherson’s part or in Brotherson’s room; but a decided one in the place where Sweetwater sat.  Objects which had been totally indistinguishable even to his penetrating eye could now be seen in ever brightening outline.  The moon had reached the open space above the court, and he was getting the full benefit of it.  But it was a benefit he would have been glad to dispense with.  Darkness was like a shield to him.  He did not feel quite sure that he wanted this shield removed.  With no curtain to the window and no shade, and all this brilliance pouring into the room, he feared the disclosure of his presence there, or, if not that, some effect on his own mind of those memories he was more anxious to see mirrored in another’s discomfiture than in his own.

Was it to escape any lack of concentration which these same memories might bring, that he rose and stepped to the window?  Or was it under one of those involuntary impulses which move us in spite of ourselves to do the very thing our judgment disapproves?

No sooner had he approached the sill than Mr. Brotherson’s shade flew way up and he, too, looked out.  Their glances met, and for an instant the hardy detective experienced that involuntary stagnation of the blood which follows an inner shock.  He felt that he had been recognised.  The moonlight lay full upon his face, and the other had seen and known him.  Else, why the constrained attitude and sudden rigidity observable in this confronting figure, with its partially lifted hand?  A man like Brotherson makes no pause in any action however trivial, without a reason.  Either he had been transfixed by this glimpse of his enemy on watch, or daring thought! had seen enough of sepulchral suggestion in the wan face looking forth from this fatal window to shake him from his composure and let loose the grinning devil of remorse from its iron prison-house?  If so, the movement was a memorable one, and the hazard quite worth while.  He had gained—­no! he had gained nothing.  He had been the fool of his own wishes.  No one, let alone Brotherson, could have mistaken his