“A native form?”

“Naw.” The short lesson on aircar use was over, but he was in no hurry to leave. “No vertebrates native to Opal. Biggest thing ashore is a kind o’ four-legged crab.”

“Is there anything dangerous out in the ocean?”

“Not to you ’n’ me. Least, not dangerous by design. When you get a ways offshore, watch for a big, green hump coming up to the surface, ’bout a kilometer across. That’ll be a Dowser. It’ll damage boats now an’ agin, but only ’cause it don’t know they’re there.”

“Suppose one came up underneath a Sling?”

“Now why’d she be dumb enough to do that?” His voice was teasing. “She come up for air and sunlight, an’ there’s none of them under a Sling. Go find yourself a Dowser — seein’ one’s a real experience. They come up a lot at this time of year. An’ you were lucky to meet that ole tortoise, you know. ’Nother few days and he’ll be off. They’re leaving extra early.”

“Where are they going to?”

“Ocean. Where else? They know Summertide is on the way, and they want to be nice an’ cozy when it comes. Must know it’s going to be extra big this year.”

“Will they be safe there?”

“Sure. Worst thing that can happen to one of ’em is he gets to sit high and dry for a while at real low tide. Couple of hours later, he’s back swimmin’.”

He stepped down from the running board on the left side of the car. “If you want to find the quickest way to the edge of the Sling, fly low an’ see where the turtles’ heads are pointing. That’ll get you straight there.” He wiped his hands on a dirty rag, leaving them as black as when he started, and gave Darya the warmest, most admiring smile. “Anyone ever tell you you walk an’ move real nice? You do. If you want company when you get back, I’ll be here. I live right near. Name’s Cap.”

Darya Lang took off wondering about the worlds of the Phemus Circle. Or was it was just in the air of Opal, the thing that led men to look at her differently? In twelve adult years on Sentinel Gate she had had one love affair, received maybe four compliments, and noticed half a dozen admiring looks. Here it was two in two days.

Well, Legate Pereira had told her not to be surprised by anything that happened outside Alliance territory. And House-uncle Matra had been a lot more explicit when he learned where she was going: “Everyone on the Circle worlds is sex-mad. They have to be, or they’d die out.”

The big turtles were not visible at the flying height she chose, but a path to the edge of the Sling was easy to find. She flew out over the ocean for a while and was gratified to see the monstrous green back of a Dowser rising from the deep. From a distance it could have been a smaller, perfectly round Sling, until the moment when the whole back opened to ten thousand mouths, and each released a hissing spout of white vapor. After ten minutes the vents slowly closed, but the Dowser remained basking in the warm surface water.

Darya realized for the first time what perfect ecological sense the Slings made on a tidal waterworld like Opal. The tides were a destructive force on worlds like Sentinel Gate, where the rising and falling ocean waters were impeded in their movement by fixed land boundaries. But here everything could move freely, with the Slings riding buoyantly on the changing water surface. In fact, although the Sling that bore Starside’s spaceport must even at that very moment be moving up or down in response to the gravitational pull of Mandel and Amaranth, it was completely at rest relative to the ocean’s surface. Any disruptive force came from third-order effects produced by its large area.

The life-forms should be equally safe. Unless a Dowser were unlucky enough to be caught in an area where extra-low tides left the ocean bed exposed, the animal should be totally unaware of Summertide.

Darya flew to a point near the edge of the Sling, far enough inland to feel comfortable, and set the car down. It was not raining there, and there was even a suggestion that the disk of Mandel might show its face through the clouds. She climbed out and looked around. It was strange to be on a world so empty of people that there was no one to be seen from horizon to horizon. But it was not an unpleasant experience. She walked closer to the edge of the Sling. The soft-stemmed, long-leaved plants that fringed the ocean were bowed down with yellow fruit, each one as big as her fist. If Cap could be believed, they were safe to eat, but that seemed like an unnecessary risk. Although her intestinal flora and fauna had been boosted on arrival by forms suited to Opal, the microorganisms inside her were probably still deciding who did what. She walked closer to the ragged boundary of the Sling, took off her shoes, and leaned forward to scoop up a handful of seawater. That much she was willing to chance.

She sipped a few drops from her palm. It was brackish, not quite sea-salt. Rather like the taste of her own blood.

The complicated chemical balance of a planet like Opal made her sit back on her haunches and think. In a world without continents, streams and rivers could not perform their steady leaching of salts and bases from upthrust deep structures. Microseepage of primordial methane and the higher hydrocarbons must occur on the seabed, with absorption taking place through the water column. The whole land-water balance had to be radically different from the world that she knew. Was it truly a stable situation? Or were Opal and Quake still evolving from their condition before that traumatic hour, forty-odd million years ago, when they had been cast into their wild new orbit around Mandel?

She walked a hundred meters inland and squatted cross-legged on a hummock of dark green.

The parent star showed as a bright patch, high in the cloud-covered sky. There would be at least another two hours of daylight. Now that she had taken a closer look at Opal, she saw it as a warm and friendly world, not at all the raging fury of her imagination. Surely humans could thrive there, even at Summertide. And if Opal was so pleasant, could its twin, Quake, be all so different?

But it would have to be very different, if her own conclusions had any validity. She stared at the gray horizon, unmarked by boats or other land, and reviewed for the thousandth time the train of analysis that had brought her to Dobelle. How persuasive were those results, of minimal least-square residuals? To her, there was no way that such a precise data fit could occur by coincidence. But if the results were so persuasive and indisputable to her, why had others not drawn the same conclusions?

She came up with only one answer. She had been helped in her thinking because she was a stay-at-home, a person who had never traveled between the stars. Humanity and its alien neighbors had become conditioned to think of space and distances in terms of the Bose Drive. Interstellar travel employed a precise network of Bose Nodes. The old measure of geodesic distance between two points no longer had much significance; it was the number of Bose Transitions that counted. Only the Ark dwellers, or perhaps the old colonists creeping along through Crawlspace, would see a change in a Builder artifact as generating a signal wavefront, expanding out from its point of origin and moving across the galaxy at the speed of light. And only someone like Lang, fascinated by everything to do with the Builders, might ask if there were single places and times where all those spherical wavefronts intersected.

Each piece of the argument felt weak, but taken together they left Darya fully persuaded. She felt a new anger. She was in the right place — or would be, if she could just leave Opal and get herself over to Quake! But instead she was stuck in a sleepy dreamland.

Sleepy dreamland. Even as those words formed in her mind there came a grating whirr from behind. A figure from a nightmare flew through the air and landed right in front of her, its six jointed legs fully extended.