Then, the sea again, storm-tossed as before, shifting here and there as Maniel sought in the immensity of sea and sky for the thing he desired. "Two hundred miles south by east of New York City," he droned. "There it is, gentlemen!" They all saw it then, in full flight, eight thousand feet above the surface of the Atlantic, traveling south by east at a dizzy rate of speed. "Note," said Kleig, "that it keeps safely to the low altitudes, in order to escape the notice of regular air traffic." No one answered. The eyes of the Secret Agents were on that flashing, bulbous-bodied plane of the strange wings. It appeared to be heading directly for some objective which must be reached at top speed. * * * * * For fifteen minutes the flight continued. Then the plane tilted over and dived, and at an altitude still of three thousand feet, the wings slashed forward, clicking into their notches in the sides of the bulbous body, with a sound like the ratchets on subway turnstiles, and, holding their breath, the Secret Agents watched it plummet down to the sea. It was traveling with terrific speed when it struck, yet it entered the water with scarcely a splash. Then, for the first time, an audible gasp, as that of one person, came from the lips of the Secret Agents. For now they could see the objective of the aero-sub. A monster shadow in the water, at a depth of five hundred feet. A shadow which, as Maniel manipulated his instruments, became a floating underwater fortress, ten times the size of any submarine known to the Americas. Sporting like porpoises about this held-in-suspension fortress were myriads of other aero-subs, maneuvering by squadrons and flights, weaving in and out like schools of fish. The plane which had bourne Prester Kleig churned in between two of the formations, and vanished into the side of the motionless monster of the deep. The striking of a deep sea bell, muted by tons and tons of water, sounded in the Secret Room. "Don't turn it off, Maniel," said Kleig. "There's more yet!" And there was, for the sound of the bell was a signal. The aero-subs, darting outward from the side of the floating fortress like fish darting out of seaweed, were plunging up toward the surface of the Atlantic. Breathlessly the Secret Agents watched them. They broke water like flying fish, and their wings shot backward from their notches in the myriad bulbous bodies to click into place in flying position as the scores of aero-subs took the air above the invisible hiding places of the mother submarine. * * * * * At eight thousand feet the aero-subs swung into battle formation and, as though controlled by word of command, they maneuvered there like one vast machine of a central control--beautiful as the flight of swallows, deadly as anything that flew. The Secret Agents swept the cold sweat from their brows, and sighs of terror escaped them all.