"But how?" insisted the reporter. "You seem to be so confident, and every one else does nothing but guess." "I'll show you quite clearly," the professor said gently, "if you'll come back to the laboratory." They moved toward the rear of the house. A hullabaloo of whistles broke out in the harbor. The girl turned toward the professor. "Teddy already?" The professor frowned. "He hasn't had time." He went to a window and looked out, inspecting the sky keenly. A slender black splinter hung suspended in the air. The professor flung open the window, and a musical humming filled the room. As they watched a smoking object detached itself from the black flyer and fell downward. "That must be Varrhus," said the professor. A winged flyer with the insignia of the American aviation corps painted on the under surface of its wings darted into their field of vision. Black smoke trailed behind it as it shot toward the sinister black craft. There was an instant's pause, and then little puffs of white mist appeared before the propeller of the aëroplane. "He's firing his machine gun!" said the reporter excitedly. As he spoke the black flyer dropped like a stone, and the American plane shot above it. Almost instantly the black flyer checked in mid-air and rose vertically with amazing speed. The American plane drove on for a second, and then wavered. It began to climb, stalled, and dropped toward the earth in a series of side slips and maple-leaf turns. It came down erratically, crazily. "Killed!" said the professor with compressed lips. His daughter uttered a cry: "And Varrhus is getting away!" The black flyer had become but the merest speck. It had attained an almost unbelievable height. Now it deliberately swung around and headed off toward the northeast with its same incredible speed. CHAPTER III. Teddy Gerrod was stuffing his feet into heavy, fur-lined arctic boots. Ten or twelve soldiers were loading clumsy, awkward-looking engines on improvised sledges resting on the ice at the foot of the fort embankments. Others were putting equally ungainly iron globes with winged metal rods attached to them on other sledges. A dozen befurred and swathed figures came down the slope of the embankment and examined the preparations. A naval launch ran smartly alongside the edge of the ice, and a messenger came over at the double to the commandant of the fort, who stood by Teddy Gerrod. The messenger saluted. "Sir, the object dropped from the black flyer was a tin float having a message attached. The smoke was from a smoke fuse, lighted to attract attention." He handed over the letter, saluted again, and retired. The commandant tore open the letter and read it through, then swore frankly.