"It's not a...grand passion. It was just something that happened. We fell into it."

"Our bed."

"Don't do the bitter sarcasm number, please."

He looked down at his hands on the table.

"Everything's going wrong," he said in a quiet voice. "Everything. I'm sorry." He took a deep breath. "It's contemptible. Inexcusable. I'm weak. I'm a liar." He shrugged and looked at her. "Now you're here, I'm baffled at myself. I can't understand what made me do it. Now you're here."

Hope thought of that moment in the park yesterday and of her upwelling of sympathy for him. She pushed her chair back and went round the table to him. He tensed as she approached. Even then she wasn't sure what she might do. From somewhere came the urge to hit him.

"Life's too short," she said, and bent to kiss his cheek.

They talked about it. Hope confessed she had been watching him for two days. He was unsettled by that news. He said he would never have expected her to be quite so devious. Hope said she would never have expected him to have an affair with Jenny Lewkovitch.

They went for a walk and had a meal in a restaurant. They tried talking about other things, then they acknowledged to each other that they were trying to talk about other things and so talked about the affair a bit more.

The day progressed with a strange lethargy.

Of all the emotions that Hope experienced, the most bizarre was a sense of disappointment. Disappointment that he could have betrayed her with someone so ordinary, so mundane as Jenny Lewkovitch. She recalled their encounter at the front door. Her awkwardness; Jenny's breezy, brazen calumnies. The cheese shop...the chitchat...she saw again Jenny's small face, her funny, pointed chin, her fringe, her bulky artisan's clothes. She tried to imagine, from a man's point of view, what there might be about Jenny Lewkovitch that could be described as sexually attractive. She failed. Perhaps it was simply a matter of mutual need and mutual opportunity?...But how dull, she thought, and how disappointing. And in any case where does that leave me?

By the evening of that slow day John's mood began to change. During the afternoon he had made an effort, had looked closely at his behavior and taken responsibility for the consequences of what he had done. As it grew dark, Hope sensed him beginning to withdraw into himself.

At half past six he switched on the television and settled down to watch a quiz show, notebook in hand.

"Why are you watching that crap?" she asked.

"I'm interested in them."

"Game theory? Again?"

"Ah...yeah. Sort of."

She let him watch. She went into the bedroom and changed the sheets. Shouldn't he be doing this? she thought, allowing herself to feel a little bitter. Shouldn't he be slightly more aware of my feelings? Surely this job was one for the adulterer, not the adulteree?...Then she told herself to calm down. The whole plan, she reminded herself with some irony, was not to pretend it hadn't happened but to get its importance-its lack of importance-in perspective....

She stuffed the sheets into a plastic bag. She wouldn't have them laundered, she thought, she would just throw them away. An expensive symbolic gesture, perhaps, but no less satisfying for all that. And she- "Hope?" John called from the sitting room.

She went through. He was still watching the quiz game intently, with the volume turned so low as to be almost inaudible. He glanced at her, then back at the screen. She waited patiently.

"I'm all ears," she said.

"I think..." He paused, eyes still on the game. "I think we should stop all this."

"What? Television?"

"This farce."

"I'm not with you."

He stood up and switched the television off.

"Us. The marriage," he said. "I can't take any more of it."

John moved out. She didn't throw him out, exactly, but at times she consoled herself with the thought that she had. In fact she left him in their flat and went back to Dorset, assuming he would be gone when she next returned.

Before she left she telephoned Bogdan Lewkovitch and said she wanted to talk to him. He suggested they meet in a cafe near South Kensington tube station. He was waiting there when she arrived. It was a dark, old-fashioned-looking place, with cracked oilcloths on the table and run by a staff of stout old ladies. They drank milky coffee from scratched glass cups.

Bogdan was a large man with fair, untidy hair and, oddly for someone of his age, he still suffered from acne; he always had a few pink spots on his neck and jaw beneath his ears. He had a brisk and direct manner and often caused inadvertent offense in the college. Hope liked him. While they talked he ate three pastries, triangular sticky cakes studded with nuts as big as gravel.

"It's about John, isn't it?" Bogdan said, almost at once, munching.

"Yes."

"What can I tell you? Each day he's different." He picked some crumbs off the table with his forefinger. "That's part of the charm, of course."

He told her that John's work on turbulence had started well but he had moved on too quickly. Conclusions he had drawn from a study of fluid dynamics he had then tried to apply more generally to all types of discontinuities. But here the sums did not quite add up. Those promising avenues were revealed as dead ends. Lucid and attractive formulae generated prolix answers of babbling complexity.

"And so he got very depressed, for a while. Which is natural. We could all see it. But then," he winced histrionically, "we all go through that. That kind of frustration."

Bogdan said that the first really bad sign was when John started working piecemeal, almost at random, on other topics-irrational numbers, tiling, topology-"even the dread world of physics attracted him for a week or two," Bogdan said, with a sarcastic smile.

"And now he's back on game theory," Hope said. She told him about the quiz show.

Bogan said that, initially, John's work had been astonishing. He had read a paper that everyone regarded as completely novel and exciting. The trouble was, Bogdan said, there were no laws of trespass in the world of science. Many people were working simultaneously, all over the world, in John's area. All types of turbulent, discontinuous phenomena were being analyzed: weather systems, economic markets, radio interference. John was not alone, he said. He ordered more coffee.

"But the cruel irony is," Bogdan said, "that those first months of work John did on turbulence seemed to have opened doors for the others, but not for John. He's like...you know, a guy who invents an engine that runs on steam but finds out that James Watt reached the patent office first." He shrugged. "Happens all the time. Even when you're dealing in nothing but abstract ideas-concepts." He snapped his fingers. "Someone on the other side of the world comes up with identical proofs."

"So. John's got so far but can't go further."

"Yeah, and it's killing him, I guess. It would kill me. You see, he thinks someone else is going to snatch the prize."

"What can he do?"

"Nothing. He just has to accept it. We all tell him, but you know, I think that's what's causing his problems."

Hope frowned. She wasn't sure if this explained why he had slept with Jenny.

"I bumped into Jenny the other day," she said. "How is she?"

Bogdan was eating. He swallowed and swilled down some coffee and then told her, with some eagerness, that they were thinking of getting divorced.

"I'm seeing someone else," he said. "In Birmingham. I'm very happy with her."

"Oh. Great."

"But, you know, I'm worried about the children, et cetera, and all that."

Hope said she understood.

"And Jenny," Bogdan said. "I think maybe she has a lover here in London. But I don't know who."

For an instant, malice prompted her, urged her to try for a small revenge, but she resisted. Instead she told him vaguely about her troubles with John and how they were going to separate for a while. There was no one else, she said, it was a question of warring temperaments. They both felt that some time apart might be the answer. Hope wrote down her telephone number in Dorset and gave it to Bogdan. She asked him to keep an eye on John.

"Let me know if things get worse," she said.

"Oh, sure. I see him every day. I'll call you."

They left the cafe. It seemed very bright outside after the brown gloom. Hope flinched as a bus thundered by. Bogdan kissed her farewell and reassured her once more.

"Everyone's getting divorced," he said wryly. He paused. "They're funny people, mathematicians," he said. "You should have married a physicist. We're not quite so crazy."

THE CALCULUS.

The calculus is the most subtle subject in the whole field of mathematics. It is concerned, I read, with the rates of change of functions with respect to alterations in the independent variable. It is the foundation of all mathematical analysis.

I'm lost. But I'm still attracted by this idea of its subtlety and importance. I like the fact that we apply the definite article to it. The calculus.

A simpler definition tells me that the calculus is the study of continuous change, that it deals with growth and decay, and I begin to understand why it is such a crucial tool. Growth, change and decay...that applies to all of us.

But its key defect, it seems to me, is that it cannot cope with abrupt change, that other common feature of our lives and the world. Not everything moves by degree, not everything ascends and descends like lines on a graph. The calculus requires continuity. The mathematical term for abrupt change is "discontinuity." And here the calculus is no use at all. We need something to help us deal with that.

The rains threatened, but still they never came. Joo and I kept up our watch on the Danube but saw no further incursions. Meanwhile, Alda logged the movements of the other members of the southern group as best he could alone.

After several days sitting in my hide overlooking the river ravine, hot and sticky and pestered with flies, I decided further vigilance was fruitless. As a result of the attack on Mr. Jeb, I assumed, Clovis had led the southern group farther south almost to the edge of the escarpment. Their core area was now a good two miles from the Danube; any patrolling northerners would have to cover a vast area of the forest in order to find them.

I was away from the camp most days from dawn to sunset. I often arrived at the canteen late, as the others were finishing their meals, and in this way managed to keep my social contacts to a minimum. After abandoning our surveillance at the river I spent a morning going over the data of Alda's follows, trying to plot the extent to which the core area of the southern group had moved and how confined it now was. It was clear at once that they were wandering about far less, spending much more time together as a group and rarely venturing off on their own or in twos. Except for Lena.

Alda had done two follows on Lena. She had left the group one day and had gone off foraging on her own. At the end of the day she had constructed a sleeping nest about half a mile from the others. She had returned to the group the next morning and then, two days later, had wandered off again. Alda had last seen her at four o'clock one afternoon high in a dalbergia tree. Since then she had not been seen. When I superimposed Lena's movements on a map of the others' it was obvious she was ranging as widely as she had ever done, oblivious, it seemed, to any risk.

The three of us spent the next two days with the southern group. There was still no sign of Lena. The other chimps seemed quite relaxed; there was no evidence of excessive caution or fear. The only significant change since I had last seen them was that Rita-Lu was now fully in estrus. We saw Clovis and Conrad copulate with her, Clovis many times, but Conrad only once. Even then Rita-Lu jumped away from him after three or four thrusts and Conrad ejaculated into midair. Rita-Lu still presented to Conrad but he seemed subdued and quiet. It was as if, with Mr. Jeb gone, Conrad had lost his natural desire. Even Muffin showed some interest in Rita-Lu but she would chase him away.

Clovis ministered to her most often. Rita-Lu's swollen, shiny rump infallibly aroused him and he would break off his feeding or grooming whenever she presented to him and squat down, thighs spread, his testicles-big as tennis balls-resting on the ground, like hairy tubers at the root of some thin, lilac-stemmed flower drilling upward toward the sun.

One morning when I met Joo and Alda they told me that a man from a village south of Sangui had informed them that he had heard the sound of chimpanzees fighting in the bush. I took out a map and they showed me where the village was. I plotted the most direct route there.

We walked south through the forest for over three hours. We were now near the edge of the lush vegetation that marked the southernmost precincts of the national park. The escarpment here took a ninety-degree turn east. Due south was a wide, flat rift valley of featureless orchard bush and small villages, scattered miles apart. The province we were in was very underpopulated and those people who lived on the fringe of the park had no necessity, as yet, to move up the green slopes of the escarpment in search of better pasture or more arable land. A few fields of maize and cassava had encroached here and there, a certain amount of timber was felled for firewood, but the human population posed little threat to the habitat of the chimpanzees.

We emerged from the treeline, tired and a little footsore, and surveyed the view spread below us. To our left the forested hills of the escarpment swung east for twenty miles and then rolled southward once more. The gray clouds of the ever-impending rains hung above the distant hilltops, but above us the sky was blue, badged with round, white, stationary clouds. The piebald, dusty bush stretched out for miles before us. At our feet lay the small nameless village with its irregular fields cut haphazardly from the bush, the green maize plantations almost indecently fresh-looking in the midst of so much dusty aridity. In the far distance a band of darker vegetation crossed the plain, the riverine trees of a tributary of the massive Cabule.

We ate our lunch. Alda pointed to the river in the distance, where it emerged from a valley cut in the hazy hills, and said, "There is FIDE. And beyond. And there"-he gestured north behind our backs-"there is UNAMO."

"Look," Joo said. "Airplane."

He pointed. I saw, coming from the west, high up, making contrails like spilled salt, two jet fighters. Migs, I supposed. I had never seen them in our skies. Usman told me they rarely flew missions in the north. They passed above us and disappeared into the haze. Seconds later we heard the rumble of their engines.

We went down to the village. Round mud huts, thatched with straw, the matting walls of compounds. Joo spoke to one of the old men lounging beneath a shade tree and a small boy was deputed to lead us to the approximate scene of the chimpanzee fight.

We crossed a patch of even waste ground. At one end a soccer goal stood, a few shreds of net still hanging from it.

"For the missionaries," Joo said. "They were here before the war."

Men and women working in the fields looked at me curiously as we walked by. Then the ground started to rise and the bush closed in on us once more. The small boy pointed to a clump of cotton trees on the edge of the ridge above us. The noise came from there, he said, and left.

It took us another half hour of further climbing to reach the cotton trees. We spread out and began to search through the grass and bushes beneath them. I found many discarded seeds of the fruit. They were nutty flat discs about an inch across, like small mango seeds, surrounded by a pale yellow, fibrous flesh in a fuzzy, suedelike casing. From the amount of seeds on the ground I would have thought that the entire southern group had been feeding here. There were many torn leaves and broken twigs on the ground as well but nothing that indicated anything more than the usual careless and untidy feeding of a group of hungry chimpanzees.

Then Joo called out. I ran over to him.

Just beneath the lowest branches of a large bush was a severed arm, the right arm of a young chimpanzee that seemed to have been crudely torn off at the shoulder. I looked at it: it could only be Muffin's. Alda was peering under the bush. He reached in with a stick, hooked it onto something and tugged. At once there was a great noise of buzzing and the bush came alive with thousands of blowflies, hard and shiny. It was as if handfuls of gravel were being flung at the leaves. The bush shivered and vibrated as the flies fought to escape. I backed away while Alda pulled his shirt over his head and plunged in to haul out the body.

It was Muffin. Something had been eating him recently, something small and carnivorous, a bush rat perhaps, and his stomach had been opened to expose his viscera, slimy and swollen. His face was battered and cut, just as Mr. Jeb's had been, and his left foot and leg below the knee was missing. The bloody, congealed socket of his right arm was filled with swarming ants. There was no stink but, as Alda heaved him out, some of his guts fell from the hole in his stomach with a moist slither.

I gagged and felt saliva swirl into my mouth. I felt faint and shocked. Muffin: neurotic Muffin who hated to leave his mother. I turned away and spat and took a deep breath. I opened my bag and removed my camera.

It was a long walk back home. I had wanted to bring Muffin's body but it was too badly torn to carry for such a long distance. As we trudged homeward I had plenty of time to think. I wondered what to do. Mr. Jeb and Muffin were dead. Lena was missing but I was now convinced that she too had been attacked and probably killed. Let's assume, I reasoned, that three of my southern chimps have been killed by the northerners. I had no doubt that Muffin was the latest victim. I had a vivid memory of Pulul sitting on Mr. Jeb's back twisting his leg round and round until the ligaments and tendons gave and it broke. The thinner limbs of a small adolescent would be no problem for a mature adult. A full-grown male was incredibly strong: I had seen them snap branches as thick as an arm with almost casual ease. They could have torn apart Muffin as easily as you or I would wrench a drumstick from a roast chicken.

Three chimps were gone; only five were left: Clovis, Conrad, Rita-Mae, Rita-Lu and baby Lester. There were seven mature males in the northern group and several enthusiastic adolescents. What chance did my depleted band have against them? And there was another problem, no less perplexing: what should I tell Mallabar? For the first time I began to regret so precipitately sending off my article to the magazine. Events had moved faster than I could ever have imagined. Suddenly, revenging myself on Mallabar no longer seemed my highest priority.

"I don't quite see what you're saying," Mallabar said, slowly.

We were in his bungalow; it was about nine in the evening and we were sitting in his study. This room was a small shrine of self-importance. The walls were covered with framed citations, photographs, honorary degrees and diplomas, but the room's furnishings were simple to the point of austerity: two metal filing cabinets, a square wooden table as a desk and a couple of canvas director's chairs. Mallabar preempted all criticism of the egotistical decor by classifying it as his fund-raising room. Important sponsors could see what results their patronage had achieved, and the spartan facilities reassured them that nothing had been squandered.

I sat in a canvas chair looking at several framed magazine covers featuring the man behind the desk opposite me. He had a faint smile on his face, but it was only a polite formality. His mood was not benign.

I began again.

"I want to take a female from the south and reinstate her in the northern group."

"Hope, Hope," he said, leaning forward urgently. "You don't understand. This is not a zoo. We can't move animals from cage to cage, as it were. To do what you want would be...out of the question. This is a wild environment. What you're proposing is an act of engineering."

I resisted the temptation to point out the engineering required to build and operate the Artificial Feeding Area.

"I still think we should do it."

"But you haven't told me why."

"To...to avert trouble." I held up my hand to stop him interrupting. "Northern males are making regular patrols into the south and-"

"I don't like that word 'patrols,'" he said.

"That is what they are," I said emphatically. "I've seen them, and..." I paused for a second, "there has been aggression."

He stiffened. "What do you mean?"

"Three of my chimpanzees have been killed. And two, for sure, have died as a result of violent attacks."

"That is a forest out there, my dear. Full of wild beasts."

I ignored his sarcasm. "I have a horrible feeling"-I was treading very carefully here-"that they have been attacked and killed by the northern chimps."