Willy-nilly, Chan and Tatty were swept out farther from the Sun, out to the hive of the Asteroid Belt where a hundred minor planets formed the commercial and political power house of the solar system. From there it was outward again, to the huge industrial bases on Europa, Titan, and Oberon. Equipped with Monitor headsets, Chan and Tatty plunged deep into the icy ammonia slush below the deep atmosphere of Uranus, to the infernal region where the Ergas — the Ergatandro-morph Constructs — worked tirelessly on the fusion plants and the Uranian Link system. The work was still three centuries from completion. Disturbingly, the Erga slaves already gave evidence that they were developing their own complex culture.

With the survey of the old solar system approaching its end, Tatty halted the program and stared at Chan. Nothing. Plants and planets, science and society, all left him equally unmoved. Sighing, she signalled for the lesson to continue.

They leaped, a trillion kilometers into the outer darkness. The monstrous bulk of the Oort Harvester was at work here, a world-sized cylinder lumbering along through the hundred billion members of the cometary cloud. Slow and tireless, at home a tenth of a lightyear from Sol, the Harvester was hunting down bodies rich in simple organic molecules, converting them to sugars, fats, and proteins, and Linking the products back to feed the inner system.

A final solar-system leap. Chan and Tatty skipped to the quiet outpost of the Dry Tortugas: arid, volatile-free shards of rock that marked the gravitational boundary of Sol’s domain. Past this point, any matter had to be shared with other stars. Sun itself was a chilly pinprick of light, while temperatures hovered a few degrees above absolute zero. Tatty stared in awe at the billion-year-old metal tetrahedra, enigmatic relics left by a race old before humanity was young.

The lesson halted. “Questions?” said a polite voice.

Tatty glanced at Chan’s impassive face. Again he was studying the hair on his wrist. “No.” She spoke for both of them.

“Then we will continue.”

So far the lesson had been a general one, designed to teach Chan the structure and varied economies of the solar system. Now it would be specific to Pursuit Team training.

The display changed scale again. Far beyond the boundaries of the solar system lay the members of the Stellar Group.

“First, the overview.” The region of accessible space was a knobby and dimpled sphere, fifty-eight lightyears across and centered on Sol. The Perimeter formed a fuzzy outer boundary where the probe ships, limited at best to a tenth of light speed, expanded the accessible region by up to ten lightyears a century. Humans had never encountered another species possessing the Martin Link. The Perimeter would remain roughly spherical, unless and until — people had talked of it for centuries — some probe ship at the Perimeter met a ship from a second bubble, blown by another species who had found the secret of the Mattin Link for themselves.

(Humans had written thousands of papers and millions of words, seeking to analyze the outcome of such a meeting, just as in an earlier era, writers had endlessly discussed possible first contact with intelligent aliens. Like those analyses, the new papers were erudite, well-argued, and persuasive — and reached contradictory conclusions.)

In the final segment of the lesson, Chan and Tatty homed in on the home stars of the known intelligent species. The Pipe-Rillas had been found first. They were stellar neighbors, with the binary stars of Eta Cassiopeiae, only eighteen lightyears from Sol, as their home system.

Next came the Tinkers, twenty-three lightyears out. Their home world was Mercantor, circling the star Fomalhaut.

After that, the discovery program had suffered a long dry spell. The Perimeter expanded steadily, reaching a new volume of space that increased quadratically with time, but no new intelligence was discovered; not until a probe reached Capella, forty-five lightyears from Earth, and found the Angels. That had been a century and a half ago. The Angel language, civilization, and thought processes were still an unlocked mystery for humans.

In the final segment of the lesson, images of each species were added to the displays. That was Kubo Flammarion’s brain child. He hoped to make Chan “feel comfortable with the aliens, before he meets them.” Tatty considered that was optimism of the highest order.

The screen first showed the quivering mass of a Tinker Composite, men the enlarged view of individual components from which the Tinker was made. They were fast-flying legless creatures about the size of a humming-bird. Each of them possessed just enough nerve tissue for independent locomotion, sensation, feeding, breeding, and clustering. Each had a ring of eyes on its blunt head, and long antennae to permit coupling into the Composite. The bodies were purple and black, shiny, sticky-looking. Tatty was fascinated. She was sorry when the display moved on to show the arthropod cylinder segments of a Pipe-Rilla, and finally the dull green fronds of an Angel. But at least this ought to interest Chan — it would interest anyone, even a child. She glanced across to see how he was reacting. He was not watching the display at all. He was staring at her.

“Chan!”

But he was grimacing, not in annoyance or boredom but in pain. He reached up to place his hands on the side of his head.

Tatty stood up at once. Chan did this sometimes after a Stimulator session, never before. “What hurts?”

“Head. Hurt bad.” He was mumbling, rubbing his temples and then his eyes. “Picture make me hurt bad.”

Kubo Flammarion had warned of critical points. They often came with headaches and they could lead to fever, nervous degeneration, and rapid death. Tatty went to kneel by Chan’s side and took his head between her hands. “Don’t move, Chan. I have to look.”

She had been told the warning symptoms. Chan sat quietly as she lifted his eyelid and shone a light on the eyeball. No reddening, no protrusion. The pupils dilated normally with the light on them. Sight, and then hearing, proved normal when she tested them.

Tatty took Chan’s temperature. That was normal, too. So were the brain rhythms of his EEC. Everything was normal. Could Chan possibly be faking it, knowing what came next?

“Do you still hurt?”

“Not bad now. Getting better.”

Tatty sighed — mixed relief and discomfort. She did not have sufficient reason to put off the thing that she most dreaded, the ritual of forcing Chan into one of the “special” sessions with the Tolkov Stimulator.

Might as well get it over with. Tatty stood up. “Come on, Chan.” She took him by the hand and led him through into the next chamber. Amazingly, he did not protest or resist. Could he be faking it the other way round — hurting, and not willing to admit it?

“Chan, are you sure you don’t hurt any more?” He would not look at her, but he slowly shook his head. “Not hurt.” He sat down in the Stimulator chair and let Tatty strap him in.

Tatty hesitated before she connected the headset. The whole thing was unfair. With no experience, she was forced to make decisions that could kill Chan.

“All right?”

Chan did not speak. Tatty turned on the power. Usually she could not bear to watch the whole session, but today she felt obliged to.

For a few minutes Chan sat quiet, eyes closed. There were frown lines on his forehead, and as he gripped the arm-rests the tendons in his forearms and the backs of his hands sprang up white and prominent.

At last he began to moan, a long, breathless sound high in his throat. Tatty knew it well. It was “normal,” if anything about the Tolkov Stimulator could be called normal, a sign that the power build-up was approaching its peak rate. There was nothing to see, but inside Chan s skull a complex series of fields was being generated in both cerebral hemispheres. Natural patterns of electrical activity were sensed by the Stimulator, modulated, and fed back at increased intensity. At the same time, the body’s own motor control was inhibited. The damping was necessary to prevent Chan from tearing himself to pieces. The jerks, spasms, and writhing of the body were still spectacular, but Flammarion had explained that they were unrelated to what Chan was actually feeling. Chan s agonies were far worse than that. They arose within the brain itself, as a pain far more intense than anything of physical origin.