McDowell put the old biplane into a dive and Tim promptly followed. Twisting and turning, they resumed the battle they had waged over the Atkinson airport. Tim was flying rings around McDowell now and Prentiss pumped shot after shot toward the biplane but the air was rough and it was hard to gauge the distance accurately. "Concentrate on his motor," Tim shouted. "We can't stay up more than five minutes more and you may be able to put his ship out of commission." Prentiss filled the magazine of the rifle again and, firing steadily, directed his bullets toward the motor of the biplane. Tim could see the black splashes as the bullets struck the cowling. There was just a chance that he might be able to disable McDowell's motor. The motor of their own ship coughed. Tim switched on the emergency tank and it barked steadily again. Their minutes in the air were numbered for he had no way of knowing whether the emergency tank was full or how much it held. "I'm going to try to bring him down," Tim yelled at Prentiss. "What are you going to do?" "See if I can't run my wheels through his prop. Hang on." "Won't that wreck your landing gear?" "We'll have to take a chance on that. If it does we'll get down someway. Are you game?" "Go ahead," said the inspector grimly. "I'll try it once. There may not be a second time." "I'll get you down all in one piece," grinned Tim. Then he turned to the job at hand. McDowell was just a little above them and about a thousand feet ahead. Gunning the motor hard, Tim climbed above their quarry and with the motor on full, dove headlong for the biplane. McDowell must have sensed what was in Tim's mind for he stood up in his cockpit and took deliberate aim with the automatic. Bullets plunked into the wing of the monoplane, but Tim kept on. Prentiss's rifle was silent for the moment for at that angle he was unable to fire. Down they dropped like an eagle after its prey. McDowell dove back into the cockpit just as the monoplane crashed down on him, the wheels of the ship above almost raking his head. Tim steeled himself for the expected crash as the propeller of the biplane bit into the landing gear but it did not come. By some trick of magic which Tim would never know McDowell dropped the biplane down almost ten feet at the last moment. Or perhaps fate had taken a hand and the ship had struck an air pocket. At any rate the monoplane sped on overhead and McDowell was safe again. "What happened?" asked Prentiss. Tim shook his head. "I don't know. Maybe the biplane hit rough air and dropped. I thought surely we had him that time." The motor coughed, rapped out a few more revolutions, and then died. "That's about all for us," said Tim bitterly. "And there goes McDowell," said the inspector.