For half an hour the grim battle went on. Then it ceased as suddenly as it had started. McDowell, giving his plane a full gun, darted away southwest. He was making a break for safety. With a heavy bank of clouds rolling up in the west, night would drop its mantle early. There was just a chance that he might remain aloft until he could find shelter in the darkness. Tim saw through McDowell's strategy at once. Undoubtedly the other had a full tank of gas and since the old trainers usually had large tanks, sufficient to keep the ancient craft aloft until after nightfall. The flying reporter glanced again at the gauge on the instrument board of the monoplane. He didn't need to. He knew what the needle indicated without looking but perhaps there had been some mistake. The gauge showed only an eighth of a tank of gas. Another half hour in the air; perhaps a little more. Then they would be forced down and McDowell would wing on alone. Tom leaned back and shouted to the inspector. "We've got only enough gas for another half hour. Want to land now, fill up the tank, and then try to overtake McDowell, or keep after him until our fuel gives out?" "Something might happen to his ship before our gas gives out. We'll keep going as long as we can," Prentiss shouted back. Tim nodded and set out in full pursuit. In three minutes he was on McDowell's tail and he throttled down. No use to push the motor any harder than necessary. The minutes droned on. Tim checked their direction. It was obvious that McDowell was heading for the border. It was a long hop; impossible in one jump, and he wondered where the pilot ahead of him intended to refuel. He probably had some out-of-the-way airport where he could come down, replenish his supply of gas and oil, and get away without being reported. Fifteen minutes went by the clock. The needle on the gas gauge dropped lower. Probably McDowell, up ahead, was chuckling for he certainly knew the amount of fuel in the monoplane he had left behind. Prentiss tapped Tim on the shoulder. "How much longer?" "Not more than 15 minutes." "Close in on him and I'll see if this rifle can't convince him that it's time to come down." Tim's right hand jammed the throttle on full and the trim monoplane leaped ahead, overhauling the old trainer rapidly. McDowell, hearing the deeper drone of the motor behind him, looked back at them. Tim banked to give Prentiss a clear shot and the federal agent pressed the trigger. Tim could hear the sharp spats of the gun as the bullets sped on their way. Holes appeared in the fuselage of McDowell's ship. Prentiss was shooting better. McDowell, pointing an automatic at them, emptied the magazine. His aim was wild and not a bullet struck the monoplane.