"Hi," he said, once he was close enough to be heard over the breaking surf.
The mysterious woman held up a hand in greeting.
"Hello. I'm Phoatri-Salmsa Dessera Kalvind Shoo dam Algravia."
"Pleased to meet you, Ms. Shoo," he answered, "Yir Refan-Haifeen, as I'm sure you already know. I take it you're the person Hub just asked me to meet?"
"I am. I'm supposed to talk to you. But not here. Hub wants to show you something first."
Refan-Haifeen raised an interrogatory eyebrow, but it appeared that Shoo was immune to this kind of treatment.
"Okay," he said, gesturing at the surf-car, "Can I offer you a lift?"
He stowed his surfboard swiftly and slipped into the rear-facing seat. Shoo bent gracefully and sat facing him.
"Where are we going?" he asked.
"Nearest sub-Plate access point."
The surf-car powered up, vibrating almost imperceptibly for a second. Then it turned and wheeled itself silently across the sand towards the mass of olive-green foliage which edged the beach.
Shoo seemed content to sit in silence. Refan-Haifeen took the opportunity to look more closely at the woman opposite. She was, he realised, old - probably well into her third century; Culture citizens aged slowly, and it was often said that it was impossible to tell a person's age with any accuracy. But there were certain tell-tale signs, more to do with attitude than appearance; older people moved with a certain hard-to-fake unconscious grace. Whatever her age, she was still a tall muscular woman, now regarding him calmly and radiating an air of composed competence. She looked like exactly the kind of person who had spent much time in Contact - perhaps even Special Circumstances - and was now being trusted with a delicate mission on behalf of the Orbital Hub.
"So, you're going to be my minder?"
"Well, I wouldn't put it quite like that," she replied, a smile flashing across her face, "I'm just trying to help, that's all."
The surf-car, now at speed, plunged into a narrow gap in the wall of foliage and followed a meandering trail up the slope towards the cliffs edging the bay, drawing smoothly to a stop in front of a low building which housed the access point itself.
Refan-Haifeen hopped out and pulled his surfboard from the stowage. Shoo disembarked on the opposite side and watched the man tuck the board under his arm.
"You're keeping that?" she asked, sounding surprised.
"I got Hub to make it for me specially. It's completely dumb: no embedded systems, no intelligence, no AG or field projectors, not even basic communications or tracking. Just a slab of foametal."
"Because, otherwise it would be cheating," he said bluntly, "The standard boards work hard at helping you on the wave, keeping you balanced when you should really wipe-out. Sure, you can tell them to stop, to turn themselves off - but even then, they'll intervene if they think you're in danger."
"And that's cheating, is it?"
"Yes, it is. These days, I'd probably make a board myself."
Shoo looked incredulous but declined to comment further.
"Shall we go?" she asked, gesturing at the entrance.
The car wheeled away, presumably to park itself somewhere convenient to await its next user. The two humans stepped into the lift which would take them to the underside of the Plate.
Culture Orbitals were a way of providing a vast amount of living space with a minimum quantity of material. A complete Orbital was a hoop in orbit around a star, a narrow band just a few thousand kilometres wide but three million kilometres in diameter, spinning just fast enough to provide one standard gravity and a standard day-night cycle. The inside surface was generally landscaped to resemble a planet, complete with mountains, deserts, savannas, lakes, jungles, tundra and a bewildering variety of geomorphological features which might have been found on any one of a thousand planets, and almost always substantial areas of ocean.
Orbitals were usually constructed incrementally, starting with an opposing pair of Plates held in position by force fields. Bulkhead ranges and Edge walls kept the atmosphere in place while additional Plates were added. Y'grath Orbital was old, long completed and had a comprehensive high-speed transport network, running on the outside surface where the vacuum of space allowed for higher velocities. While a person could choose to travel by boat or aircraft or any of innumerable kinds of surface transport - where the journey was itself part of the experience - the quick way of getting to another part of an Orbital was to use the sub-Plate cars. This also provided a splendid view of the underside of the Orbital, in order to admire the dips and bulges which formed the basic shapes of mountain heights and ocean deeps on the other side.
The lift dropped rapidly, slowed to pass through two pairs of single-aperture concentrically rotating airlocks, then accelerated briefly before arriving at the rapid-transport level. The doors slid open to reveal a waiting travel-car, its hull milkily-translucent and its airlock open, and one of Hub's physical representatives standing nearby.
Like many Orbitals, the Hub Mind of Y'grath Orbital deployed humanoid Avatars, but made no attempt to make them even passably human. These sexless, impossibly slender, silver-skinned beings provided an instantly recognisable point of interaction for the human population with the Mind which oversaw every aspect of their lives.
The Avatar gestured economically with one arm towards the open airlock. The three of them entered, Refan-Haifeen wedging the board carefully behind the bench seats which had just malleabled their way out of the floor before sitting next to Shoo; the silvery being seated itself opposite. The lock closed noiselessly, and the car set off, sliding out from the access point and accelerating smoothly.
"So, where are we going, Hub?" Refan-Haifeen asked.
"There's a particular spot on this Plate I want you to see," the Avatar replied.
The walls, ceiling and floor all turned transparent. Above, and to both sides, a view of the blackness of space, brilliant points undimmed by light from the local star, here blocked by the structure of the Orbital. Below their feet, the vast black plain of the base material flowed smoothly, the corrugations which formed the surface features just visible. Refan-Haifeen suspected that the windows were performing some subtle image enhancement for their benefit.
"Here it is now," it added, tapping the walls gently.
Approaching on one side was a region on the Plate which was faintly glowing a dull red, barely visible even with whatever processing being applied. The spot enlarged to fill half the view, whatever enhancement processing presumably now working at maximum. Even so, it was largely featureless, with just a suggestion of sluggish movement.
"What is it?" Shoo asked.
"I don't know," the Avatar replied flatly.
Both Shoo and Refan-Haifeen turned to stare at the silver being.
"You don't know?" they said in unison.
The Avatar held up both hands.
"No, I don't," it said, sounding peevish, "I've been asked, very firmly, not to stick my metaphorical nose into whatever it is that is generating enough heat to seep through several tens of metres of Plate material."
"And you've promised not to?"
"It's very hard not to so promise, when you're asked by a member of the Interesting Times Gang."
Shoo raised a couple of highly expressive eyebrows.
"Interesting Times Gang?" Refan-Haifeen asked, "Let me guess. Special Circumstances?"
"Yep," the Avatar replied, "So I have to assume they'd spot any attempt by a mere civilian machine such as myself to probe more closely. Any drone or gelfield-suited human I might send would be identified as such before they could get close enough to observe anything useful. And I wouldn't want to be seen to be breaking my promise to the ITG."
"But you still really want to know what it is?"
"Have you any idea how violated I feel," the Avatar almost squeaked, "When a Mind takes on the task of running an Orbital like this, it's a great responsibility. It is my duty and my pleasure to maintain a safe and stimulating environment for everybody, to care individually and collectively for every part and every being in my jurisdiction, to support varied ecologies and the flora and fauna which goes with them, to provide a garden, a theme party, an amusement park, an adventure playground tailored to the preferences and desires of all."
Refan-Haifeen noted Hub was careful not to describe it as a zoo, even though this might be a truer representation of the relationship between Culture Minds and the humans and other biologicals.
"If there is something there which might present a danger to the Orbital or to anything on it," the Avatar concluded firmly, "Then I want to know everything about it."
Refan-Haifeen suddenly looked thoughtful.
"Where is it?"
"We're underneath the Great Grafikic Ocean," the Avatar responded promptly, "That spot is right in the middle of the Azular Deeps."
"Ah. Now I understand. So you want me - us," he added, gesturing at Shoo, "To go take a look. And in a distinctly low-tech way."
"You? Why?" Shoo demanded.
"I've got this hobby," Refan-Haifeen answered obscurely, "And, if I was to guess, plausible deniability."
The Avatar looked smug. "Just so."
"Okay, so I've seen enough. Heard enough," Refan-Haifeen announced, "You can let me off anywhere."
"What? Are you going to help me here?" the Avatar demanded.
"Maybe," he said with a shrug, "I'm considering it."
Shoo looked nonplussed.
"What are you going to do now?" she insisted.
"Go to a party," he answered, collecting his surfboard, "And think about what you've told me."
He looked down again at the dark irregular plain which was, on the other side of the super-dense Plate material, the deepest point on the ocean. Then he turned back to Shoo.
"Do you want to come?" he asked, suddenly earnest, "To the party?"
She frowned momentarily.
"Sure, why not?"
"Can you swim?" he asked.
"Yes, of course. Why?"
"This is a surfer's party. A free-diver's party. It'll be, well, pretty wet."