When the next day broke a bloody conflict was raging between the two turnpikes, the French infantry attack on German trenches preceded by a terrible artillery bombardment, a storm of shell and shrapnel. Colonel Muller beckoned Billy to his side. They stood together on the heights from which the French had been expelled only the day before. "My boy," was the brisk address of the officer, making a field-glass survey of the smoke-crowned landscape, "I am going down the line, and I am to do the distance in an aëroplane. Is it you or Schneider who will do the driving?" "You gave me the first call yesterday," reminded Billy. "That was my intent, and it still holds. I was only seeking to learn if you were of the same mind since that powder mill let loose down there." "I well know the odor of it," stoutly maintained Billy, "and it doesn't weaken my knees." The young aviator, accepting the matter as settled, hastened toward staff headquarters. "Mr. Roque," he excitedly called, "Colonel Muller wants to try one of the No. 3's this morning, and I'm to pilot." The secret agent lifted his eyebrows as though surprised, but he really was not. The arrangement had already been made. "Say, Buddy, this is rough that we can't both go; and suppose something should happen to you?" Henri had just realized that something was up, in which his chum was vitally concerned. "Don't you worry, pard," consoled Billy, "it is only a little spin of a few miles, and we'll be back in no time." "Wish it was me," sighed Schneider, for this firebrand guessed that it would be a red-hot journey. As the biplane swept into the breeze current, trending to the river, which then was running brimful, and in many places overflowing its banks between the two armies, Colonel Muller advised Billy to keep the machine climbing for the time being, as a terrific fusillade was in progress in the distance of the next two miles, the shells hurtling through the air like lighted express trains. In the three steep-sided ravines that deeply notched the plateau on the east French troopers swarmed like bees, and at this cover the big German guns were blindly banging. "We can't see much, Colonel, at two thousand feet," complained Billy. "You would see nothing at all if we ran into one of those fragments of shells," coolly suggested the officer, "but never mind, you will do some diving in a few minutes." Billy got the signal to dip at the juncture of the turnpikes, and to hold a level and lower course along the line of battle, marked here by infantry fighting between the seemingly crawling columns far below. "Down!" The colonel's order was peremptory, and Billy forthwith volplaned toward the earth. CHAPTER IX. THE LUMINOUS KITE. THE biplane had hardly scudded its length on the turnpike, when the colonel leaped from the machine, his sudden appearance greeted by salvos, both of cheers and an extra round of rifle discharge.