And she turned and stepped to the middle of the street, where Billie had already marked a large number of flying-machines. In fact, the space from curb to curb was practically filled with them, all neatly parked. Without exception they were ornithopters; that is, machines built on the bird-wing principle, sustaining themselves by a flapping motion rather than by air-pressure due to a propeller. Their size varied from one-seater affairs of very small size to craft large enough to hold a score. Most were gaudily painted. The surgeon's own machine was a two-seater, small but powerful in design. She stepped up a short ladder into a comfortable cockpit, provided with a folding top, which at that time was laid back out of the way. She proceeded to adjust various levers and hand-wheels, glanced at certain dials, touched a button, and immediately the craft took flight, its wings beating the air with a dull leathery rhythm which drowned out the faint clanking of the machinery. A moment later the flier was high above the street. To Billie's disappointment, the surgeon did not glance down enough to tell the architect whether the street belonged to a city of any size. Instead, her agent drove carefully through the traffic, which Billie would have called dangerously dense. She remembered that she had seen nothing but aircraft in that street; no automobiles at all. And then the flier was rushing through the air at a lively rate. Billie caught quick glimpses of innumerable machines, few of which were moving in the same direction as the surgeon's. A few minutes more elapsed, and then Billie was experiencing a much higher level, with the machine flying at what must have been a tremendous velocity. Shortly it was all but alone in the sky. After a while the surgeon's eyes made out something far below, which puzzled Billie exceedingly. It seemed to be a ship under full sail; only, so far as she could see the craft was resting upon clouds, not air. It was still a long way ahead. And then Billie was given a glance aloft, where she saw another craft, a small flapping affair like the surgeon's. It was just rising on a long slant so as to cross above her course. And at that very instant there came a sharp crack, followed by a splintering crash. The surgeon's flier lurched heavily to one side. Next second the woman was staring at her left wing. It was broken about the middle and thrashing wildly. Another instant, and a part of the thing came loose, flew off, and struck the surgeon on the top of her head. A muffled cry, and then blackness came. And the next thing Billie saw was the emergency ward of Smith's great skycruiser, with the surgeon, blinking as she recovered, looking up into the smiling face of her big blond rescuer. V CAPELLA'S DAUGHTER