"Don't you hold the thought for a moment, Henri, that you could catch the Calais weasel asleep. Oh, I say, there's a concert on downstairs," quickly concluded Billy, as the notes of violin and piano were wafted above. "Let's hunt the music." A high tenor voice was merging into the accompaniment when the boys reached the floor below, and they saw that the singer was one of the curly-lock type, and in evening attire. What of the eyes, though, that gleamed upon the Aëroplane Scouts as they stood in the doorway--the artistic make-up could fool them, but there was no mistaking the smiling orbs under the blackened eyebrows. Fox tracks were mixing again! CHAPTER V. WHEN THE LIGHTS WENT OUT. THE vocal efforts of this new favorite had called forth round after round of applause, for good music never went amiss in Teuton territory. Among the vigorous hand-clappers the boys noted a well-groomed man, apparently about forty, wearing an affable manner and the best clothes that the continent can produce. Henri nudged Billy. "Size up Roque, won't you, please, and isn't he a dandy?" Billy was first inclined to doubt the identity of their taskmaster, who a couple of hours ago was a far cry from being in the glass of fashion. Never before had the boys seen him in that sort of rig. "You're dead right, Henri, it is the old scout. He's a corker, sure!" This note of admiration had scarcely sounded when Roque was joined by a slender, wiry individual, also set up as a swell, with a shock of sandy hair, and sporting a monocle. The fellow with the quizzing glass had apparently moved to get a better view of the singer, as well as to get in touch with the secret agent. "Wonder if that's the man who spotted Anglin on the parade ground at Hamburg?" "Don't let your imagination run away with you, Henri," advised Billy, who in speaking was careful not to indicate that his attitude was anything but careless. The sandy-haired man was taking the same precaution, but Henri, nursing the idea that would not down, was more and more impressed with the belief that the elegant figure was seeking the measure and not the music of the warbler at the other end of the room. If the singer had sized up the situation, it had not affected his rendering a bit of light opera that was just then exciting an encore. There was nothing at all the matter with his German or with his voice. Nobody apparently was more delighted than Roque, and he appeared to be expressing his opinion to the wiry listener beside him. The latter bowed politely and then sauntered toward the revolving door leading into the lounging section of the hotel, fingering a cigar as he proceeded. Henri edged around nearer to the piano, the player of which was completing the program with a national air, the melody of many voices aiding the performance.