New York lay below them. The long, straight lines of lights shining up through the semidarkness of the moonlit night made a strange appearance to the two in the swift machine. Davis had mounted to a great height, some ten thousand feet, and the pin points of light outlined more than a dozen cities and towns. The Hudson was a faintly silvery ribbon flowing down placidly from a far-distant source. Because of the ice cake in the Narrows its level had risen two or three feet, but now it flowed smoothly over that great obstacle, melting and carrying it away toward the sea. The fighting plane roared around in huge circles, seeming strangely alone in the vast expanse of air. One searchlight from below moved restlessly about the sky. A second joined it, then a third. One by one a dozen or more of long, pencil-like beams of light shot up into the sky and moved here and there in seeming confusion, but actually according to a carefully prearranged plan. A hooded red light showed below the biplane in which Teddy and Davis were awaiting some sign of the black flyer. That had been agreed upon, and none of the searchlight beams flashed upon the circling machine. From time to time Davis shut off the motors, and the two of them lifted the ear flaps of their helmets to listen eagerly for the musical humming that would herald Varrhus' approach. Far to the east they could see where the faintly luminous waters of the ocean came up to and stopped at the darker masses of the land. The harbor below them glittered in the moonlight. The only peculiarity in the scene was the absence of the little harbor craft that ply about busily by day and night upon their multifarious errands. They were all securely docked. The wharves, too, were dark and silent. All the maritime industry of New York was at a standstill. A wide spiral to twelve thousand feet. The motors were hushed during a two-thousand-feet glide, while the two men in the machine listened intently. For two hours this maneuver had been repeated and re-repeated. No sound save the rush of the wind through the guy wires and past the struts had broken the chilly stillness of the heights. The sky was a blue dome of a myriad winking lights. A pale silver moon shone down. The nose of the machine pointed down and the motors ceased to roar. Faintly but unmistakably above the whistling and rushing of the wind about the surfaces of the biplane a deep, musical humming could be heard. Abruptly the motors burst into life again. The exhausts began to bellow out their reassuring thunder. The machine began to climb again, circling to every point of the compass, while Teddy and Davis scanned the sky keenly for a sign of the black flyer with its cargo of menace to New York. "I'm going to fifteen thousand." Davis' voice sounded with metallic clearness in Teddy's ear. The telephones between the two helmets were working perfectly. "That was Varrhus, all right?" said Teddy quietly. "Did you signal to the people beneath?"