"The rest of the story," concluded Quinn, "is a matter of history. How the fleet bottled up the harbor at Vera Cruz, how it was forced to send a landing party ashore under fire, and how seventeen American sailors lost their lives during the guerrilla attack which followed. All that was spread across the front pages of American papers in big black type--but the fact that a steamer named the _Ypiranga_ had been held up by the American fleet and forced to anchor at a safe distance offshore, under the guns of the flagship, was given little space. Apparently it was a minor incident--but in reality it was the crux of the whole situation, an indication of Germany's rancor, which was to burst its bounds before four months had passed, another case in which the arm of Uncle Sam had been long enough to stretch halfway across a continent and nip impending disaster." "But," I inquired, as he paused, "what became of Dawson and Stewart?" "That I don't know," replied Quinn. "The last time I heard of Jack he had a captain's commission in France and was following up his feud with the Hun that started in Mexico City four months before the rest of the world dreamed of war. Dawson, I believe, is still in the Department, and rendered valuable assistance in combating German propaganda in Chile and Peru. He'll probably be rewarded with a consular job in some out-of-the-way hole, for, now that the war is over, the organization to which he belongs will gradually dwindle to its previous small proportions. "Strange, wasn't it, how that pair stumbled across one of the first tentacles of the World War in front of a cafe in Mexico City? That's one beauty of government detective work--you never know when the monotony is going to be blown wide open by the biggest thing you ever happened upon. "There was little Mary McNilless, who turned up the clue which prevented an explosion, compared to which the Black Tom affair would have been a Sunday-school party. She never dreamed that she would prevent the loss of millions of dollars' worth of property and at least a score of lives, but she did--without moving from her desk." "How?" I asked. But Quinn yawned, looked at his watch, and said: "That's entirely too long a story to spin right now. It's past my bedtime, and Mrs. Quinn's likely to be fussy if I'm not home by twelve at least. She says that now I have an office job she can at least count on my being round to guard the house--something that she never could do before. So let's leave Mary for another time. Goodnight"--and he was off. IV THE CLUE ON SHELF 45 "Of course, it is possible that patriotism might have prompted Mary McNilless to locate the clue which prevented an explosion that would have seriously hampered the munitions industry of the United States--but the fact remains that she did it principally because she was in love with Dick Walters, and Dick happened to be in the Secret Service. It was one case where Cupid scored over Mars."