"Of either fact you may learn by following instructions. You are to bring both biplanes, early morning, and circle over the city. In the south section you will note tall column with figure on top in center of square. Back of same is elevation on which rise two towers. Watch these. If one flag shows, hold over high road running west; if two flags, sail north and land at lodge house where canary sang for us. There wait. If highroad route (one flag), see red scarf signal for drop. When you read and commit these lines destroy." "What a system that old fox controls," observed the reader. "Killing one of his men didn't close the show in Warsaw. Do you get all this, pard?" "I think I do," asserted Henri, "but let me go over it again to be sure." Both boys having Roque's communication pat in their minds, Billy tossed it into the flames of the nearest campfire. The aviation lieutenant serving with the division gave them free reign and all possible assistance in preparing for their flight. He asked no questions. Crossing the river, the young aviators ascended to great altitude, hardly visible to any casual ground view, and taking lower levels gradually over the city. Each with an eye on the compass, the pilots mentally rehearsed their instructions. Operating in unison, though a hundred yards or more apart, they checked speed when sighting the burnished tower tops showing above all other structures on the south line, first identified by the tall column and its surmounting statue in the square. The aërial maneuvering continued for a seeming quarter of an hour, and while the sun rays splintered on the glistening turrets over which they were keeping vigil, no other manifestation appeared. Through this long exposure to the danger of attracting unwelcome attention, the boys were momentarily expecting some aëroplane demonstration from the Russian military camps showing to the east. On the highroad, finally, the aviators saw two horsemen galloping their mounts towards the hill, and then lost to view between the twin bases of the towers. A flag swung out from one of the tiny windows under the gilded domes. One flag: The signal to hold over the road, which stretched whitely for a mile or more and merged into the fertile fields without the city. The red scarf next. Would it call the suspended biplanes in swift swoop to the earth? Skilled hands gripped the levers in readiness to instantly respond to the signal. A cart with two muffled figures in it rumbled leisurely down the road. There was no urging of the sorry steed straining at its belled collar. The biplanes perceptibly lowered, though it was merely guess work on the part of the aviators. The movement of the cart might have been just one of ordinary traffic, the occupants just plain, everyday peasants.