She walked through Blacknoll farmyard. It was empty apart from a damp, bedraggled collie that picked its way through the brown puddles, barely glancing at her. The tearing noise of a drill biting into metal came from a big asbestos barn. It was funny, she thought suddenly and for no particular reason, but she wasn't missing sex. Weeks had gone by since the last time she and John had made love but she wasn't missing it at all.

She was still pondering this phenomenon as she unlocked her cottage door and changed out of her damp clothes. She put the kettle on the Raeburn's hob to boil and wondered vaguely if this was a sign that, genetically, she was old maid material. Perhaps she was exhibiting the symptoms prematurely?...This is what Meredith claimed had set in with her recently. Except in her case she wasn't the least worried about it. In fact she was almost exultant: complete contentment with one's own company, Meredith said, was a rare and real achievement. Every need-emotional, intellectual and physical-could be catered to, single-handedly and fullfillingly, by the correctly inclined person. Blissful self-sufficiency was how she described it.

Hope recalled the last time she had stayed with Meredith, after the disaster of Ralph's seventieth birthday party. The next morning she had watched Meredith's routine carefully. First came the leisurely descent from the bedroom about nine, still wearing nightdress and dressing gown; then the radio was switched to the Radio 3 station and turned down low. The juice of three oranges, freshly squeezed and chilled with ice cubes, was gulped down standing at the sink. Then came the move to the kitchen table with a pot of coffee, two slices of brown toast and lime marmalade and a packet of cigarettes. There was no conversation. A newspaper, the Telegraph, was glanced through briskly and then folded back to the crossword. Then Meredith sat, drank coffee, smoked and did the crossword until it defeated her or she defeated it, a period that tended to last approximately half an hour.

Hope had looked at her hunched over her paper, cigarette held at her right ear-a cursive rope of smoke climbing to the ceiling-a slight smile or a frown on her face depending on what progress she was making with the crossword. It was as if she were stimulating her brain cells for the day ahead, like an athlete warming up before a race. It was a ritual-and sacrosanct-Meredith said, the best time of the day.

Hope wondered if she could ever be like that, or if, conceivably, she already was? Could she achieve that state of contented self-absorption day after day, month after month. But even if she could, did she want to? She remembered Meredith's warning about the Curse of Brains. Was this its other face, the compensatory benefaction: the ability to enjoy being alone?

Hope chopped carrots and onions and prepared the other ingredients of her powerful stew. When it was on the hob and cooking, she opened a bottle of claret and put some music on. She sat down in front of the fire with a glass of wine and a novel, and as she read she smoked a cigarette. So far, so good, she thought. This was all right. No complaints.

The phone rang.

It was Bogdan Lewkovitch.

"What's wrong?" she said.

"It's John, I'm afraid. He's ill."

THE CLEARWATER SET.

This is difficult. This is not straightforward. The Clearwater Set. I said it to John as if I knew what I was talking about. I had fanned the glowing embers of his ambition with my casual remark but I had no idea what the Clearwater Set was or what it was capable of.

And how he wanted it! How he longed for his name to merit a separate entry in dictionaries of mathematics. "John Clearwater, English mathematician, inventor of the Clearwater Set." But what was it? Or rather, what would it have been? The answer is: a simple formula. A formula that would fix an endless series of points on a complex plane. From the reiterated numbers that the formula would generate-like grid references and coordinates on a map-you would be able to plot an image on a piece of paper or a computer screen. If you plotted the image that John's numbers gave you, an extraordinary shape would emerge. It was magic.

He tried to explain it to me once, using an old analogy.

What are the dimensions of a ball of string, he asked me? The answer is: it depends on your point of view. From a mile away a ball of string will appear dimensionless. A point. A full stop. Moving closer you can see that the ball is three-dimensional, solid, shadowed. Closer still and the ball has resolved itself into a two-dimensional mess of filaments. Place a filament under a microscope and it transforms itself into a three-dimensional column. Magnify that-hugely, monstrously-and the atomic structure of the filament is revealed: the three-dimensional thread has become a collection of dimensionless points again. The short answer is: the position and scale of the observer determines the number of dimensions of a ball of string.

The Clearwater Set, John told me, would be able to reproduce this subjectivity endlessly. He was trying to write a simple algorithm that would reproduce the magical, infinite variety of the natural world. Extreme complexity would emerge from the simplest formula.

Or put it the other way round: behind all this teeming variety would lurk one simple instruction. For some reason I understood it better expressed in that manner. I could see what excited him. He always said that the most profound joy for any scientist was when the abstract workings of the mind found a correspondence in nature, in the world we live in. This was as true for a mathematician, he said, as for any chemist or physicist. That moment, he said, was the most acute of all the intellectual pleasures available to man.

A set, a ball of string, magnificent variety and complexity governed by a simple rule. I could not understand the detail of what John was doing but I could see the direction in which he was headed. To weld the world of mathematics to the world we live in; to blend pure abstraction with the randomly concrete. If he could write the Clearwater Set he could die happy. But as I realized this much, I saw that the final stages were eluding him. He had gone so far and then stopped. He urged himself on but remained fixed and immobile. It was as if he had single-handedly invented the internal combustion engine but his mind finally balked at the design of a carburetor. The assembled mass of components sat there on his laboratory bench, inert, waiting only for the final touch to roar into animated life.

Clovis had a cut on his ear, but otherwise both he and Rita-Lu seemed unscathed by the attack I had heard, but not actually witnessed. It had scared them, though. The remnants of the southern group huddled together constantly now, never wandering off any distance alone. As they foraged for food they were noticeably more watchful and jumpy. They would survey a prospective feeding area for up to an hour before advancing forward to eat, never lingering for long. Even now, resting, Clovis flat on his back, Conrad grooming Rita-Lu, Lester gamboling around Rita-Mae, annoying her, Conrad would pause for a while, every now and then, and look around, listening for unusual noises.

I heard a faint crackle of static on my walkie-talkie. I had the volume turned low, so as not to alarm the chimps. I backed off, out of earshot. It was Alda.

"They are comin', Mam."

"How many?"

"Eight. Nine."

"OK. Get Joo. Come down here as fast as you can."

I felt a burning, like indigestion, in my esophagus, and a cold agitation seized me. I recognized the symptoms: I used to experience them with John at his worst moments. It was the physical correlative of a crucial indecision, a growing panic of inertia in the face of several demanding options. What should I do here? Should I frighten away my chimps, run at them waving my arms?...But if I did that, all those months of habituation-or trust-would be gone at once, at a stroke, and I would never get close to them again. One part of me encouraged this course of action, but I knew all it would do was postpone events, or possibly make them worse. At least here, with the four adults grouped together, they provided more of an opposition to the northerners. The chimps sprawled in the shade of three piper trees-small trees with drooping branches that cast good shade-oblivious to the approaching danger. I waited anxiously with them: perhaps they would not be spotted this time.

I waited for forty minutes. Then Conrad heard something. He rose up on his hind legs and spread his arms, his fur bristling. The other chimps immediately prepared to move. They milled around waiting for Clovis to lead them, but he seemed uncertain and confused, uttering soft pant-hoots.

Then Darius charged out of some bushes above them, upright, teeth bared, arms windmilling. He bounded powerfully into and through the group, knocking Conrad violently out of the way. The other northern chimps followed close behind, screeching and screaming. I saw Pulul, Gaspar, Americo and Sebastian.

The two groups faced off, displaying, roaring and grimacing at each other. Darius charged at Clovis, followed by Sebastian and Pulul. There was a confused scrum of flailing arms and legs in a cloud of dust as the four chimps fought. Then they had Clovis pinned down. Pulul bit his leg and tore a long ribbon of skin off his thigh.

Meanwhile, the others advanced, led by Americo. He grabbed Rita-Mae and threw her to the ground, sending Lester flying from her back. Americo stamped viciously on her head. Rita-Lu, at the same time, crouched shivering, presenting her pink, swollen rump to the other males. Suddenly their aggression waned, became halfhearted. Then Clovis, by some mighty effort, broke free from Darius and Sebastian and leapt into a piper tree. He snapped off a branch and shook it at the northern males, his hair erect, screaming shrilly.

All fighting stopped and a sudden calm descended. Lester ran to Rita-Mae, Conrad crept under the piper tree. Only Rita-Lu was left surrounded. The males gathered round her, inspecting her rump, touching and smelling. Then all at once the northern group was off, with Rita-Lu running with them, up a small gulley and into the trees. I could hear their whoops and screechings and the hollow reverberations as they drummed on the treetrunks they passed.

Two days later Joo saw Rita-Lu return to the group. She was unhurt and was welcomed back unequivocally. Joo led me to where he had left them feeding. The same watchfulness was there but otherwise nothing seemed to have changed. Only Clovis was obviously in some discomfort; the shred of skin that Pulul had torn from his left thigh dangled like a garter from his knee. The pink flesh that was exposed looked raw and smarting. Clovis constantly interrupted his feeding to dab the wound with bunches of leaves and grass.

Then I saw something else that made me even more alarmed: Rita-Mae seemed to be developing a sexual swelling; the skin on her rump was markedly pinker and looked stretched and shiny. Theoretically, she was still anestrous, still lactating. Lester was too recently born for her cycle to have resumed. But it was not unheard of for a lactating female to experience infertile sexual swellings for some years, before her cycle properly restarted. Infertile or not, it made no difference to a male chimpanzee. I felt a sudden deep pity for my southerners. Now there would be two females in estrus. I looked at Clovis, Conrad and Lester and wondered how long these males, mature and immature, had left to live. Much though I disliked the idea, I thought I should go back and see Mallabar again.

Since the leopard had been killed, Mallabar had been exceptionally cordial toward me, with the relief of a man who had doubted for a while but had had his faith convincingly restored. My other colleagues, however, and by contrast, had grown more guarded. They were not entirely sure what had been going on, but it was clear to them in some way that I had been rocking the boat, generally making trouble. I would have to be watched more closely.

So I went to Mallabar's bungalow again, that evening after our meal. Roberta was leaving as I arrived. I noticed she had touched her eyelids with blue, and there was a sweet talcy smell of perfume about her.

"Ah, Hope," she said, a little inanely, as if I were exactly the person she expected to encounter on the Mallabar threshold. I smiled back and said her name, Roberta, in a falling cadence. She held the door open for me. I went in.

Ginga was there too. She went to the kitchen to make me a cup of coffee. Mallabar flourished me into a seat.

"I want you to do me a favor," I said, not wasting any time.

"Of course."

"Spend the next few days in the southern area with me."

"Hope," he said, a little wearily. "Really, I thought we-"

"No. There are some things you should see for yourself." I felt surprisingly tense. I sat on the edge of the chair, rigid.

"All right, all right." He spoke calmly and looked at me with some curiosity. "Do me good to get back in the field."

Ginga reappeared with the coffee and stopped in the doorway.

"Everything all right?" she said. "Hope?"

"Hope's asked me to spend a few days with her in the south," Mallabar said, talking about me as if I were slightly simple.

Ginga nodded. "Good," she said. "Excellent. You haven't been out in the field for a while. Do you good."

I spent the next three days with Mallabar as we watched the five survivors of the southern group going about their daily business. He asked me what had happened to Clovis's leg. I said I had no idea. We observed, we followed, we logged the data on the survey sheets and in our journals. Mallabar reminisced about the early days at Grosso Arvore. He told me about the efforts he and Ginga had made to habituate the chimps to their presence. It had taken him ten months to get within twenty yards of a chimpanzee without it running off. He talked of how, for the first three years of their married life, their home had been an army surplus tent. How months could go by without seeing another soul. At first I wondered if these memories, unprompted by me, were a series of oblique rebukes; if he was gently reminding me that half his life had been spent at Grosso Arvore, in these hills and forests, and that my allegations were jeopardizing everything he had set out to achieve. But after a while I realized it was genuine nostalgia. Indeed, he was quite good company and it was fascinatingly instructive to observe the chimpanzees with him. I saw that he had an understanding of these apes that was profound and, there was no other word for it, full of love.

He looked at Clovis and remembered him as an infant. He knew his siblings and how his mother had died. He had seen Rita-Lu the day she was born. He had photographed Conrad's white sclerotics as he had peered through a screen of grasses one day, and had produced thereby one of the most haunting covers ever seen on National Geographic. And for the first time, too, I really sensed the personal bafflement and hurt in him, caused by the schism in the community he had studied for so long. For unknown reasons, some of those chimpanzees that had happily swarmed round his banana-dispensing machine had suddenly lost interest in it and had migrated south. He hadn't seen Rita-Mae-or SF2 as he referred to her-he said, for over two years. Baby Lester, he confessed, he had only known through photographs. To me he seemed like the benevolent chief of a tribe grown too large and complex for him to understand. Its motivating forces, its factions and feuds, allegiances and enmities, were too difficult to quantify and relate to. He confessed as much to me one afternoon.

"It was all very mystifying," he said. "Terribly upsetting, really." He laughed. "I just couldn't understand why they were doing this to me. And to be suddenly confronted by your ignorance when you felt you knew everything-well, nearly everything. It shakes you up, I tell you."

"King Lear," I said.

He looked at me. "Good God, let's hope not. What an analogy."

"No, it was just...that same sense of mystification. Getting something so wrong. I know what you mean."

"Do you?" He smiled; he was thinking of something else. "That's a comfort."

On our second morning out Joo led us to a cluster of sleeping nests far south of the Danube. The northerners had spent the night here, he said. I realized the colonization was entering a new phase; now the chimps were not even bothering to return home as night fell.

"It's not surprising," Mallabar said. "They know there are too few chimps to use this area to the full. It was the same when we had the polio epidemic. The core area shrunk, more chimps came down from the north."

We were walking through the forest to the blasted fig tree. I was hoping we might find some northern chimps there. It was too close to the Danube, now, for my southerners. It was a sticky, still afternoon. The occasional breeze brought with it the wet-earth smell of impending rain.

"It'll rain tonight," Mallabar said, inhaling deeply. "I love that smell." He glanced at me and smiled. "I'm glad you asked me out, Hope," he said. "I'm going to do this every two months or so-spend a few days in the field-I'm losing touch." He went on almost garrulously to berate himself for the amount of administration and paperwork he was obliged to do. A manager was what he needed, he said, which would allow him to spend more time out in the bush with the chimpanzees.

The blasted fig tree was empty, but chimps had been there recently, as the ground was covered with half-eaten fruits. I paced about feeling edgy. Northerners feeding in this tree, which I had come to associate so much with my chimps.... It was almost like having your house burgled. This was my territory, mine and my southerners; now it was home to strangers and no longer felt the same.

On the third day the northerners attacked again. It had rained in the night, as Mallabar had predicted, and the forest was wet and visibly steaming in the sunlight, the paths mushy beneath our feet. We wore lightweight oilskins and Wellington boots. Occasionally we could hear the distant noise of thunder but Mallabar still wasn't sure, he said, if this was the true start of the rainy season.

Joo had located our southerners in a grove of lupus trees. The fall of rain had brought out their pale yellow, sticky flowers overnight, and all the chimps were sitting in the branches grazing on them. Rita-Mae lay on a low branch, on her back, one leg dangling, with Lester squatting on her stomach. She seemed to have eaten her fill; from time to time she would reach out, pluck a lupus flower and give it to Lester to eat.

The forest was still dripping from the drenching it had received. Everywhere was the sound of water falling on leaf as the movements of the chimps shook droplets free. And in the background there was still the noise of thunder, as the night's cloud systems moved south toward the coast, heavy furniture being shifted in the room above. We sat and watched the chimps in the sultry, moist heat. The atmosphere was soporific. Mallabar yawned again and again. It was infectious; we both yawned simultaneously.

He turned and smiled at me, and seemed about to say something, when he was interrupted by a crash of vegetation. Pulul or Americo-it was too sudden for me to tell-hurled himself out of the nearby bushes and leapt up and grabbed Rita-Mae's hanging leg. With a scream she and Lester fell the ten feet to the ground. To the left, Sebastian and Darius were up another tree after Conrad, who brachiated recklessly from his position into an adjacent tree, missed his grip and half-fell, half-tumbled through the branches to the ground.

Meanwhile, Gaspar had grabbed baby Lester by one leg and was whirling him round and round in midair. Observing this, Darius jumped down and seized the baby from Gaspar, who readily surrendered him.

Darius held Lester by both legs and thrashed him violently against the knobbled length of an exposed root. I saw Lester's skull literally explode under the force of the blow and bits of brain and bone were scattered widely. Then Darius thwacked the limp body against a trunk two or three times before flinging it carelessly away.

Conrad and Clovis made their escape, shrieking and calling. Rita-Lu adopted her half-crouched, presenting position and watched as Pulul and Americo and a couple of unidentified adolescents pummeled and stamped on the supine body of Rita-Mae, who had been badly stunned by her fall in the first charge. Then, as if on some invisible signal, they stopped and gathered round Rita-Lu. Darius drummed on a tree and they were off again, like the time before, running and whooping, Rita-Lu in their midst.

Rita-Mae was not dead. When they had gone, she stood up, shivering, and immediately fell over. She made a feeble hooting noise as if calling for Lester. She rolled over, managed to regain her feet once more, cast around a couple of times as if making a cursory search for Lester and then loped off with some awkwardness into the undergrowth after Clovis and Conrad.

The fight had lasted only a few minutes. I felt myself begin to unfreeze. I looked round at Mallabar. His face was sallow, bloodless; his beard looked suddenly black and coarse. He was biting his bottom lip, staring in front of him as if he were in terrible shock. I touched his shoulder; I could feel it shuddering beneath my fingers.

"Jesus," he said. "Jesus Christ." He kept on repeating this.

I thought it best to leave him alone for a moment or two and went to look for Lester's body. I found it hanging in a thorn bush. The head was a loose bag of pulped tissue and bone, the small limbs bizarrely mishapen and broken in many places. Carefully, I lifted him out and placed him on the ground. I turned; Mallabar was walking toward me.

He stared, clearly horrified, at Lester's body.

"Did you see," he said, in a small voice, "that alpha male, what he did? Did you see?"

I felt enormously sorry for the man. "I know," I said. "It's very shocking. Nothing prepares you for the violence. Even me."

"What do you mean?"

"This is the third fight I've seen."

"Third?"

"Yes." I spread my hands apologetically. "Eugene, this is what I've been trying to tell you. This is what's been happening here."

"Been happening?" he said distractedly, as if lost in other thoughts.

"I've been trying to tell you. But you-"

He raised his fist to shoulder level, arm bent and took a step toward me.

"What have you been doing here?" he said in an urgent, trembling voice. "What have you been doing to them?"

"What're you talking about?"

"It's you. It's something you've done to them."

"Come on, Eugene, don't be stupid!"

He lowered his fist and hung his head for an instant.

"I blame myself," he said. He looked up. "I should have had you supervised." Then he screamed at me, madly: "What have you done! What have you done?"

I took a step back. I had felt his spit on my face.

"I haven't done a thing, you fool, you bloody idiot!" I shouted at him, angry myself. "I've just been watching them." I pointed at Lester's broken body. "It's what they're doing. They're killing each other!"

He had raised his fist again. His eyes were wide.

"Shut your fucking mouth!" he shouted. "Shut your fucking mouth!"

"No! The northern apes are wiping out my southerners. One by one. Now you've seen it with your own eyes, you stupid bloody fool, and you-"

He tried to hit me. He hurled a punch, full force, at my open face. If he had connected he would have broken my nose. Squashed it flat. Crushed bones and shattered teeth. But somehow I managed to jerk my head away and down and the punch hit me on the shoulder. I heard, distinctly, the knuckle bones in his fist crunch and break as the force of the blow spun me round and right off my feet. I fell heavily to the ground. My shoulder burned, hot with pain. I felt it had sprung from its socket. I grunted through clenched teeth, flinching, looking round expecting another attack.

Mallabar was some distance off, scrabbling in the undergrowth looking for something. He was flicking his right hand curiously, fingers spread, as if they were wet and he was trying to shake water from them. He stood up; he had a stick in his left hand. He ran over toward me.

"Eugene!" I screamed at him, "Stop, for Christ's sake!"

I ducked.

He hit me across the back. The stick broke under the blow, but, because it was left-handed, it hadn't as much impact as it might have. He grabbed at me, and I pushed wildly at his face, scratching. At the same time, somehow, I caught hold of two of the broken fingers on his right hand and pulled them back with as much savage effort as I could muster.

He bellowed with pain and let me go. I ran.

I sprinted off down the path through the dripping forest toward the camp. I thought at first I could hear his running footsteps behind me, but I never looked round. I ran for fifteen minutes and then halted, doubled over, my body aching with effort. I sank to my haunches, hand on a tree trunk for support. I tried to calm down.

I felt a hot drumbeat throb in my right shoulder. I slipped my jacket off and unbuttoned my shirt. My shoulder was pink, flushed and already slightly swollen. I could see four darker circles in a row, the imprint of his knuckles. Very gently, I eased my shoulder joint. Very sore, but mobile.

I dressed and headed off again. I crossed the Danube and walked into camp past the feeding area. I could hear the noise of chimps coming from it. I turned left to cut past Mallabar's bungalow, making for the census hut. On my left were the garages and workshops. I saw a Land-Rover parked there with its bonnet up and Ian Vail leaning inside fiddling with the engine. He stood up, wiped his hands on a rag and closed the bonnet with a vengeful but satisfied bang. It had been Vail's turn to do the provisioning run this week. By rights he should have left hours ago.

"Hi," he said, as I walked over to him. "Bloody fuel pump."