And I knew, as we fought like two wharf-rats under a pier-end, that I was right. I knew that my cause was the cause of law and order. That knowledge gave me both strength and a boldness which carried me through even when I saw my writhing and desperate thief groping and grasping for his hip pocket, even when I saw him draw from it a magazine-revolver that looked quite ugly enough to stampede a regiment. And as that sodden-leathered night-hawk went placidly rolling up Fifth Avenue we twisted and panted and grunted on its floor as though it were a mail-coach in the Sierras of sixty years ago, fighting for the possession of that ugly firearm. How I got it away from him I never quite knew. But when I came to my senses I had him on the cab floor and my knee on his chest, with his body bent up like a letter U. I held him there while I went through his pockets, quietly, deliberately, one by one, with all the care of a customs inspector going through a suspected smuggler. I had no time to look over his wallet (which I remembered as being as big as a brief-bag) or his papers, nor had I time to make sure how much of the jewelry he wore might be his own. The one thing I wanted was the pearl necklace with the pigeon-blood ruby. And this necklace I found, carefully wrapped in a silk handkerchief tucked down in his right-hand waistcoat pocket--which, by the way, was provided with a buttoned flap to make it doubly secure. I looked over the necklace to make sure there could be no mistake. Then I again wrapped it up in the silk handkerchief and thrust it well down in my own waistcoat pocket. "Get up!" I told the man on the cab floor. I noticed, as I removed my knee from his chest, what a sorry condition his shirt-front was in and how his tie had been twisted around under his right ear. He lay back against the musty cushions, breathing hard and staring at me out of eyes that were by no means kindly. "You couldn't work it!" I said, as I pocketed the revolver and, having readjusted my own tie, buttoned my overcoat across a sadly crumpled shirt-front. Then for the first time the thief spoke. "D'you know what this'll cost you?" he cried, white to the lips. "That's not worrying me," was my calm retort. "I got what I came after." He sat forward in his seat with a face that looked foolishly threatening. "Don't imagine you can get away with that," he declared. I could afford to smile at his impotent fury. "Just watch me!" I told him. Then I added more soberly, with my hand on the door-knob, "And if you interfere with me after I leave this cab, if you so much as try to come within ten yards of me to-night, I'll give you what's coming to you." I opened the door as I spoke, and dropped easily from the still moving cab to the pavement. I stood there for a moment, watching its placid driver as he went on up the avenue. The glass-windowed door still swung open, swaying back and forth like a hand slowly waving me good-by.