From below she saw each one had three slits in parallel on the body, flared to take in air. These resembled gills and shone bright pink, bloodrich. As their wings lifted, she saw the slits drawn wide, three thin mouths yawning. As their elegant downstrokes began, that action forced the gills shut. Flying, breathing machines.

Masoul had been right. The Ythrians had big barrel lungs, a passive system resembling humans’. Their secret lay in those supercharger gills, probably evolved from some amphibian-like ancestor. Those livid mouths worked in heaving, bellows fashion as the flight muscles contracted and big arteries sucked the air directly into the bloodstream. Higher-air-intake organs let them burn their fuel as fast as necessary. But to see it alive, in majestic flight—!

Rachel sighed and thought, Smart birds. I wonder how it feels to be so deeply alive….

She concentrated on funneling down through the updraft layer rising along the walls. Arrowing down against the warm breezes from the vents below, she skimmed off to land with some redeeming grace on a takeoff platform. She looked up and the Ythrians were spiraling down, taking their time, still watching her. Had she proved herself in alien eyes? Hard to read those big, gold-flecked spheres, with bony ridges above them but not eyebrows.

She wanted to look unconcerned, so she gazed up at the view, hands on hips. This was the big, newest void, honed with an antibaryon fusor burst that rendered rock to plasma and lava, then vented the hot gruel through the top knothole. Media had showed all humanity the Lunar volcano show, as the ruddy rock flowed with liquid grace above the Lunar highlands, jetting into space in rosy filaments. Some grabby robo devices had caught it to shape habitats on the surface; the voids were an industrial miracle with real profits to be had. The fusor eruption had left behind this oblate spheroid twenty kilometers high and five wide, cooling quickly into a hollow pink egg.

Lunar subsurface sculpture was getting so adroit the engineers could shape any space you wanted. Rumors circulated that some rich magnate had ordered up a pyramid-shaped space, but even a fusor couldn’t do that. This big void was for flying, a unique Lunar pleasure for poor ground-bound primates. Hundreds of people were winging it as she looked up, most of them watching the aliens do astonishing feats. Fraq came by, flying upside down with effortless grace, eyeing her on the ground as he shot across the void.

Those eyes—piercing, even at this distance. His golden-brown feathers covered but did not conceal the rippling muscle. Or that he was male. Their flimsy robes flapped tantalizingly from the carry harness they wore. The Ythri could lock the joints of their limbs at will, and on Luna, 0.17 gravs, seemed to defy gravity’s existence for long, leisurely arcs. Their forewings—much like Earth birds—had humerus, radius, and ulna; these locked together in flight, giving the Ythris a look of utter unconcern as they did the impossible.