"We've four hours before dark. We'll have to set to work." Teddy went over and stepped up the ladder that leaned against the cockpit. "I want to see your gasoline supply," he remarked. In a moment he came down, looking a trifle dubious. "If I'm right about Varrhus using liquid hydrogen for a weapon, and we can set it afire, we'll dive through half a dozen sheets of flame to-night. Something will have to be done to protect that gas tank from catching fire, and some protection for the carburetors, too." "We'll fix that in a hurry," said Davis briskly. "Oh, Simpson! Come here!" In twenty minutes there were half a dozen mechanicians at work, and Teddy was carefully inspecting the machine gun at the bow of the fusilage. Teddy telephoned back to Evelyn what he anticipated would occur that night and his own share in it. "Of course there's some risk in it," he finished, "but I guess we'll come out." Evelyn's voice was more anxious than Teddy had expected. "Do be careful, Teddy," she said in a worried tone. "Please be very careful. Varrhus has so many fiendish weapons. I'm terribly afraid." Teddy's voice was grim. "With the kind assistance of the German government," he remarked, "we have a few fiendish inventions, too. I'm using explosive bullets only to-night. Varrhus is outlawed." Evelyn spoke almost faintly. "But take good care of yourself, please, Teddy," she urged. "It were better that Varrhus got away this once than that you should be killed for nothing." Teddy smiled. "I've no intention of being killed, Evelyn, but I have some intention that Varrhus shall be." There was a curious sound from the other end of the wire. "But--but----" Evelyn's voice died away. "I'm--I'm going to be praying, Teddy. Good-by." The last was very faint. Teddy turned from the instrument and went out to where the aëroplane had been rolled from its shed. The sun was sinking and dusk was falling. Time passed and darkness settled down upon the earth. Stars twinkled into being. A long searchlight poked a tentative finger of light into the sky. "We'd better be going," said Davis thoughtfully. "We want to be well up before he appears." Teddy clambered up to his seat and adjusted the straps that would hold him in place. He pulled down the helmet and fitted the telephone receivers securely over his ears. A telephone was necessary for communication with Davis, four feet behind him, because of the tremendous roar of the engines. He took the machine-gun butt and found the trigger, then made sure the first of a belt of cartridges was in place. He settled back in his seat as the mechanics began to twirl the propellers. He was going out to fight the black flyer, but most incongruously he was not thinking of Varrhus at all. His thoughts dwelt with strange intensity upon Evelyn. CHAPTER VIII.