"That is a fact," said Austin; "this new gun is a terror." "But he has no' hit any one," insisted Tam; "it's luck that he has no', but it's the sort of luck that the flyin'-man has. To-morrow the luck may be all the other way, and he'll bring doon every one he aims at. Ma idea is that to-morrow we've got to get him, because if he makes good, in a month's time you won't be able to fly except at saxteen thoosand feet." A light broke in on Blackie. "I see, Tam," he said; "so you were just hanging around to discourage him?" "A' thocht it oot," said Tam. "A' pictured ma young friend William von Archie shootin' and shootin', surroonded by technical expairts with long whiskers and spectacles. 'It's a rotten gun you've got, Von,' says they; 'can ye no' bring doon one wee airman?' 'Gi' me anither thoosand shots,' gasps Willie, 'and there'll be a vacant seat in the sergeant's mess;' and so the afternoon wears away and the landscape is littered wi' shell cases, but high in the air, glitterin' in the dyin' rays of the sun, sits the debonair scoot, cool, resolute, and death-defyin'." That night the wires between the squadron headquarters and G. H. Q. hummed with information and inquiry. A hundred aerodromes, from the North Sea to the Vosges, reported laconically that Annie, the vicious sister of Archie, was unknown. * * * * * Tam lay in his bunk that night devouring the latest of his literary acquisitions. Tam's "bunk" was a ten-by-eight structure lined with varnished pine. The furniture consisted of a plain canvas bed, a large black box, a home-made cupboard and three book-shelves which ran the width of the wall facing the door. These were filled with thin, paper-covered "volumes" luridly colored. Each of these issues consisted of thirty-two pages of indifferent print, and since the authors aimed at a maximum effect with an economy of effort, there were whole pages devoted to dialogue of a staccato character. He lay fully dressed upon the bed. A thick curtain retained the light which came from an electric bulb above his head and his mind was absorbed with the breathless adventures of his cowboy hero. Now and again he would drop the book to his chest and gaze reflectively at the ceiling, for, all the time he had been reading, one-half of his brain had been steadily pursuing a separate course of inquiry of its own; and while the other half had wandered pleasantly through deep and sunless gulches or had clambered on the back of a surefooted bronco up precipitous mountain-slopes, the mental picture he conjured was in the nature of a double exposure, for ever there loomed a dim figure of a mysterious anti-aircraft gun. He took up the book for about the tenth time and read two lines, when a bell in the corner of the room rang three times. Three short thrills of sound and then silence.