Katherine gazed up at the distant green canopy. Monkeys chattered and parrots cawed, but she couldn't see a thing - so much for the exotic wildlife of the Amazon! She pictured Professor Collier enjoying the cool British Autumn, and cursed him roundly. What with the heat, humidity, and lack of sleep, the constant irritation of the mosquitoes...

A muffled exclamation made her turn. John Pangborn was enjoying this expedition as much as she, it seemed. She stifled a grin at his red-faced discomfort - perhaps the mosquitoes had a saving grace after all.

"Bloody things!" He flailed ineffectually at the black cloud buzzing round his face. His khaki trousers had lost their pristine creases, and sweat now darkened two thirds of his shirt. Beneath the bush hat, long blond hair stuck slickly to the back of his neck.

Pangborn belonged in air-conditioned comfort. The luxurious Manaus Tropical Hotel had suited him down to the ground - here he was like a fish out of water. Except that the fish would be a piranha, she thought wryly. That pose of English gentleman was deceptive.

"What are you looking at?"

Katherine shrugged off his belligerence. "Nothing." She shifted the heavy backpack into a more comfortable position, and turned back to the narrow path between the trees. It looked well worn - an Indian trail perhaps?

A few yards ahead, João Quadros was talking to the mestizo tracker, his hands gesturing, eyes shining. At least the Brazilian zoologist was in his element. The tracker listened intently, nodded once, then went on alone.

"Not far now, senhora," said Quadros, as Katherine reached him. His heavy accent fascinated her. "There's been a recent sighting in a clearing close to here. I've sent Juscelino to check it's safe." Large, white teeth flashed in the dark face. "The moment of truth, eh?"

"About bloody time!" Pangborn stumped up to join them, wiping a sodden handkerchief over his sweating face. His pale blue eyes were overbright, almost feverish. "These conditions are bloody primitive." He took a long swallow from his canteen.

Katherine was worried by the change that had overtaken Pangborn in the last two days. She wondered if he was ill. The trip up the River Negro was one thing - the humic acid in the water deterred mosquitoes, and the boat cabins were air-conditioned - but the deep forest was something else. In these inhospitable conditions, the man's already thin veneer of civilized behaviour was rapidly eroding.

"Ready?" asked Quadros.

Katherine nodded, and Pangborn grunted, pocketed his handkerchief and slung the canteen strap over his shoulder.

"Let's go."

They followed Quadros in single file, and with a suddenness that was almost shocking emerged into a large clearing. One minute they were in verdant shade, the next in dazzling sunshine.

Like some jungle bloom, Katherine instinctively tilted her face towards the sunlight. She closed her eyes and savoured the warmth on her cheeks. The deep gloom of the jungle had become oppressive, an eternal sauna from which there was no respite. Then there was the overpowering smell, of things damp and rotting, which made her constantly feel she was about to sneeze. It had made her slightly claustrophobic, she realized, as she enjoyed the light and space. She took a deep breath, consciously relaxed her neck and shoulders, and glanced at her surroundings.

It looked like one of the gigantic Brazil nut trees had recently come crashing down, bringing other smaller trees with it. The resulting gap in the canopy had permitted sunlight and rain to reach the undergrowth. Already a layer of lush grasses and creepers almost obscured the tree trunks. Juscelino sat placidly on one of the stumps, chewing tobacco. With him were two Indians.

The way the forest natives could abruptly appear and disappear never ceased to disconcert Katherine. At the start of the expedition, Juscelino had spread word there was gringo money to be had for information on the Yeti - referred to by the natives as 'mapinguari' - and many Indians had come forward, palms eagerly outstretched. Some sightings were pure invention, she was convinced, but others seemed genuine.

She didn't recognize the tribal markings of these two - they weren't remotely like the half-westernized Indians who lived on the fringes of the river. Opaque eyes gazed at her out of stone faces. I bet they play a brilliant game of poker, she thought.

Quadros addressed the tracker. "Muito bem?"

Juscelino nodded. The Indians muttered a few words, and he translated and pointed. Quadros listened, frowning with concentration.

Pangborn pressed forward eagerly. "Have they seen the mapinguari?"

"One moment, senhor," said Quadros. He ambled across the clearing, studying the ground. Eventually he stopped at the place indicated by Juscelino's finger and squatted.

Katherine followed and peered over his shoulder at what looked like a heap of droppings. The perfect brown-and-green speckled spheres reminded her of cannon balls. Quadros found a stick and gently poked one of the turds; the outer crust flaked off exposing a moist interior. Bacteria and insects were already at work, and an acrid smell drifted up, making Katherine sneeze loudly.

"Shit," snorted Pangborn beside her. "So what?"

"Look at the size of it." As she realized what the droppings could be, the skin on the back of Katherine's neck prickled.

Quadros beckoned to Juscelino. "Vehna ca, por favor," and the mestizo obediently came over. They spoke for a moment in low voices, then Quadros straightened.

"The droppings were made by no animal he knows."

Pangborn finished recklessly gulping water from his canteen and wiped the back of his hand across his mouth. "The mapinguari?"

Quadros shook his head. "No. The natives aren't frightened enough. If the mapinguari were here, they would be miles away."

Pangborn scowled.

"I thought I'd already explained what we're after, Mr Pangborn," said Katherine, annoyed he couldn't see how important this find was. "Professor Collier believes a species of mylodonts - giant ground sloths - thought previously to be extinct, may have survived in the Amazon basin. The mapinguari sightings may really be a garbled account of these mylodonts."

"You don't agree?" Quadros picked up the doubt which had crept into her voice.

"Some elements of the mylodonts and mapinguari match. The impervious skin for example; palaeontologists have found small bone nodules embedded in Pleistocene mylodont skin remains - a primitive form of armour plating if you like. But other things don't match at all - like the mouth in the mapinguari's belly, and its single eye. Collier tried to explain away the discrepancies, but..."

"Don't lecture us, woman. We're not your students." Pangborn stumped to the far side of the clearing.

Katherine bit back a retort. He shouldn't have come, she thought sourly. It was obvious scientific research bored him rigid. But back in London Collier had greedily encouraged Pangborn's obsession with the so-called 'Brazilian Yeti', and once the resulting substantial cheque had been cashed, it was too late to refuse his request to join the expedition. What was that saying about the devil and a long spoon? Damn Collier, and damn the weak heart which had made him delegate the trip to her. Being in the tropics was bad enough without having to put up with a boorish, obsessed, glory hunter on the edge of a nervous breakdown.

She took a deep breath and continued. "I thought Collier was clutching at straws until a few moments ago. But these droppings really could belong to a giant ground sloth..."

"Do you believe in the mapinguari, senhora?" asked Quadros quietly.

She shook her head. "The Indians believe in lots of jungle spirits, don't they - a 'Father' for every animal. That doesn't mean they exist. As far as I'm concerned, the mapinguari is just a bogey-man used to scare the young and impressionable. And it has absolutely nothing to do with the mylodonts."

"If the forest tribes say it exists, who are we to accuse them of lying?"

Quadros smiled to remove the sting from his words, but Katherine knew she had been reproved. And by a fellow scientist too. Surely he couldn't mean what he had just said?

Juscelino muttered something to Quadros and pointed.

"He says there are also tracks, senhora. Look."

The indentations had been hidden beneath fresh growth. In the mud and moss, Katherine saw a clear print of three forward facing toes, and one opposing thumb. She caught her breath. A sloth would leave a print like that.

"Can we get on with it?" Pangborn had come back to see what was keeping them. He tapped his Rolex pointedly. "The sooner we find the mapinguari, the sooner I can get out of this godforsaken place."

Quadros instructed the tracker. Juscelino nodded, then set off at a brisk pace, the two Indians loping alongside him, as though out for a relaxed afternoon jog.

As they left the clearing and entered the gloom once more, Katherine tried to analyze what they had found so far. "From the depth of the footprint I'd say the ground sloth must be at least six feet tall."

Quadros nodded.

"I came all this way to find the mapinguari, not some bloody sloth," objected Pangborn.

"If it's a previously unknown species, perhaps we could call it Pangborn's Sloth," suggested Katherine. But the ploy to appease him failed miserably; he snorted and ignored her.

They had been following the tracks for nearly an hour, when Quadros stopped without warning, and Katherine almost cannoned into him.

"What is it?" she whispered as Pangborn came up beside them.

Quadros pointed to where Juscelino and the Indians now crouched. The tracker was making hand signals, and the zoologist nodded his understanding. "There is something up ahead. Something big. We must be very quiet," he instructed. "Do as I do." And placing his feet very carefully, he moved silently forward.

As she followed, a faint crunching noise became louder, and Katherine felt a chill of anticipation. She reached Juscelino and gazed in the direction he indicated.

It was another clearing, larger than the last. A clump of cane grass grew tall and lush. Two massive animals were uprooting the stems, raising them to their mouths with huge paws, and delicately using their tongues and lips to strip the juicy foliage. The crunching was the sound of busy teeth.

Even while her eyes took in the amazing sight, Katherine's scientific brain was analyzing and categorizing. The same height and bulk as an elephant, she estimated. Covered all over in greybrown fur with a tinge of green - perhaps accounted for by the presence of algae? A small head with tiny ears and a ruminant's snout. She watched fascinated as mobile lips mouthed and nibbled the greenery. Each animal had four limbs and a massive tapering tail; the two hind limbs were substantially larger than the others. Each limb terminated in three digits and one opposing thumb. As she watched, one of the creatures used a huge thumb claw to lever up a clump of bamboo.

"The Professor's mylodonts?" whispered Quadros.

"Without a doubt."

Pangborn said nothing, but his face began to flush.

"In the Pleistocene, the ground sloths probably grew even larger," murmured Katherine. She lowered her pack carefully to the ground and reached inside for her video camera. If she was to provide evidence of their existence... One of the giant sloths stopped eating and glanced in her direction. Juscelino hissed a warning, and she froze in panic, but after a moment the animal placidly resumed its feeding. Of course, with no living predators, it believed there was nothing to fear.

Carefully, she raised the camera to one eye, focussed, and began to film, praying that the motor whine wouldn't disturb the sloths again.

"And Collier believes the Indians mistook these for the mapinguari?" asked Pangborn suddenly. He sounded aggrieved.

"Yes." She continued to film, hoping he would shut up.

"I can't see any stomach mouth. How did he explain that?"

She sighed. "A gland of some kind. Producing a chemical which disorientates the watcher."

"A hallucinogen?" whispered Quadros, intrigued.

"I guess so."

"And that's his explanation for the missing single eye too, is it?" Pangborn's voice was louder and his eyes glittered.

"Keep your voice down," she hissed. Juscelino glanced anxiously at her, the Indians remained impassive.

"And what about its bright red hair?" Pangborn was shouting now, and the ground sloths had stopped eating in mid chew, clumps of bamboo sticking out of their mouths. Ears pricked with curiosity, they began to peer round for the source of the noise. "Well, I don't buy it. Collier is talking out of his arse."

Quadros put a restraining hand on Pangborn's arm. "Senhor. Please keep calm. You will make the animals nervous, and a nervous animal is dangerous." The two Indians suddenly frowned at each other.

Pangborn shook off Quadros and began to delve feverishly inside his own pack. "Thought he could use my money to prove some theory which any two-year-old can see is half-baked, did he? Thought he could fob me off with bloody sloths instead of the real mapinguari." He pulled a revolver from his pack, cocked it and aimed it at the sloths.

"For God's sake." Quadros leaped forward, but he was too late. A gunshot rang out, and chaos erupted. Katherine caught it all on video.

The nearest giant sloth squealed piercingly as the bullet scored a deep furrow along its ribs then ricocheted into the trees. A streak of red marred its fur but the bone nodules must have saved it from worse damage. For a moment it seemed frozen with shock and pain, then it turned in fury and thundered across the clearing towards the watchers. The Indians vanished into the trees like smoke.

Her camera shaking violently, Katherine continued to film. It wasn't that she felt particularly brave - her legs wouldn't move. Convinced she had only seconds left, she could at least get footage of the sloths in motion - it might enable the Institute to determine the bone and muscle construction beneath the skin...

The charging animal lumbered to a halt and reared above her, bellowing defiance. Then, unexpectedly, it turned and ran in the other direction. Its fellow diner went with it.

"Thank God," she breathed raggedly and stopped filming. Her legs felt shaky.

Juscelino and Quadros had by now wrestled the cursing Pangborn to the ground and disarmed him. Juscelino was sitting on Pangborn's stomach, but the prisoner had stopped struggling. Instead he was muttering something under his breath.

"Crazy man," panted Quadros, climbing to his feet, the gun clutched tightly in one hand.

Katherine put down the camera and stooped to listen to the murmur.

"Not the mapinguari, not..."

"Pangborn, it's me, Katherine. Can you hear me?" There was no response. She slapped him lightly across the face. Still no reaction. She slapped him harder. This time he snarled and gave her a glance full of smouldering fury, then the blue eyes blanked out once more, as though a shutter had fallen. She stared at him, shocked by the venom she had seen.

"Heat exhaustion," suggested Quadros, feeling the man's forehead. "He's burning up. Give me his canteen and some salt tablets."

While she rummaged in Pangborn's pack, the murmur started again. But this time the content had changed.

"Where is it? Must find..."

"What saying he?" asked Juscelino in fractured English. Pangborn suddenly convulsed and stretched, throwing the momentarily offguard tracker clear. And before the others could react, the Englishman gave a cry of triumph and darted into the jungle.

"What the hell?" Katherine still held Pangborn's canteen. "He's unarmed, without food or water. We must do something."

Quadros nodded. "Don't worry, senhora. We'll find him. He's following the sloths, and they'll be easy to track. Vamos." Juscelino picked himself up, then ran after Pangborn. Quadros and Katherine grabbed their packs and followed him.

The panicked giant ground sloths had left a trail of torn branches and churned earth which even Katherine could identify. Juscelino and Quadros ploughed on, heedless of the branches whipping across their faces and the heat and humidity, until Katherine felt faint and was forced to call a halt. As she bent to ease the stitch in her side, and gratefully gulped in air, she realized belatedly that the sounds of the jungle had faded to nothing. What had been a constant cacophony was now an unearthly silence. A chill ran down her spine.

"Do you hear it?"

Quadros frowned. "Yes, senhora."

For the first time since she had met him, Juscelino looked scared. "Senhor Quadros," he pleaded. "Muito mal." Then he seemed to panic and grabbed the zoologist's arm, tugging him back the way they had just come. Quadros gave an exclamation and shook the tracker off.

"What's going on? What did he say?" asked Katherine, alarmed.

"Something very bad." Quadros looked round warily.

She glanced around too, but this part of the jungle looked exactly like the rest. She was just turning to question Quadros again, when suddenly, clear as a bell in the overpowering silence, there came an eerie cry. It was like nothing she had ever heard before.

"What was that?" she asked, the pulse in her temple pounding furiously. "It sounded almost human."

"Noão sei." Quadros's face was a frozen mask, but a nerve in his cheek twitched.

Juscelino grabbed his arm again. "Muito muito mal," he said urgently. "Mapinguari. Vamos."

"Mapinguari?" Katherine was startled.

The cry came again, louder and more prolonged this time - and recognizable. The sound of a man in pain and terror.

"Pangborn!" Instinctively, she started to run towards the sound.

"Onde vai, senhora?" Quadros grabbed the back of her shirt roughly and pulled her to a stop. "Don't be stupid. You don't know what danger there is."

"Let me go. Pangborn's got himself in some kind of trouble. We can't just stand here and do nothing."

The horrible cry came again, but this time it ended abruptly in a series of gurgles and sobs. The silence it left behind seemed even more oppressive than before.

For a long moment Quadros gazed at Katherine, then he sighed, released her, and pulled out Pangborn's revolver. "As you wish, senhora."

No amount of pleading would make the tracker accompany them, so Katherine and Quadros crept on without him. They soon came to a clearing, and Quadros touched her arm.

"Careful."

She nodded wordlessly. All over her body the skin tingled, and she could feel the hairs slowly standing up one by one. She glanced up at the canopy, but the tiny patches of visible sky were a clear blue - no sign of a thunder storm to account for the buildup of static. This is just like a nightmare, she thought, wishing she could wake up.

A massive, fallen tree blocked the view, but she had the distinct impression there was something in the clearing ahead of them whose attention it would be best not to attract. She took a long, slow breath to steady her nerves, then slowly she peered over the top of the tree trunk.

The creature had its back to them. It was fully ten feet tall and covered in shaggy red-brown hair. Its straggly arms and legs, topped with oversized hands and feet, made it look something like an orangutan - but it was much too big for that. It was clutching what looked like a lifesize rag doll. Katherine watched it tear off one of the doll's limbs. Loud crunching noises filled the clearing and she wondered what it was doing. Then it turned, and she saw, and fervently wished that she hadn't.

The creature was stuffing the leg into a gaping maw in its belly - a maw which moved and seemed to have teeth. Under her horrified gaze, the thigh disappeared, then the calf, and finally the booted foot.

"Mapinguari," breathed Quadros beside her.

The creature suddenly looked in their direction, and Katherine held her breath, aware that Quadros had done the same. The huge single eye stared balefully at them for a full minute, then the mapinguari turned away. Almost casually, it pulled off the doll's head with a wet tearing noise.

Bile rose up the back of Katherine's throat, and she desperately tried to stifle her nausea. Don't think about what the doll used to be, she ordered herself, and took several breaths until she had regained control. If only she had the courage to use the video camera - but the noise might attract the thing's attention again... She eased herself down into hiding behind the tree trunk. Quadros sank silently beside her and squeezed her arm encouragingly. At length the crunching noises ceased, and gradually the sounds of the jungle returned.

They waited another half hour before daring to peer over the trunk once more.

"It is gone, senhora."

As Quadros spoke, there was a soft rustling in the trees. Katherine started as a tall Indian man materialized beside them. His face and arms were stained with red-brown fish dye in the Kayapo manner, and he wore only a short loin cloth.

Quadros showed his palms in a gesture of friendship. The man gazed impassively at them, then spoke briefly. The zoologist frowned with concentration.

"What is he saying?" asked Katherine.

"It is hard to be certain," he said. "This dialect is Juscelino's speciality. I think he is telling us to leave."

"That's all very well. But the mapinguari... What if it comes back and picks up our scent. It might follow us!" Even the thought of it made her heart race and palms sweat. She felt the native's gaze on her face. He spoke again.

"He calls it 'the Father of the sloths'. It is a jungle spirit and only hunts those who hurt its children." Quadros shrugged. "I can't understand the rest."

"So, since we didn't hurt the sloths - unlike Pangborn - we should be safe?"

"That's the theory."

"Thank God." But there was something Katherine felt bound to do before they left. She clambered over the fallen tree trunk and walked into the now deserted clearing.

She needed proof that it had been Pangborn who had died - evidence that this had not been just a jungle fevered dream. She began to quarter the clearing, combing the bloodstained undergrowth thoroughly. And then the glitter of something shiny caught her eye. Pangborn's Rolex. She picked up the wristwatch, and studied it. On the reverse was an inscription - 'JP'. Little enough to show for a man's life, she thought sadly, even if he was a complete bastard. She returned to the waiting zoologist. The Indian had disappeared once more.

"He said Juscelino is that way - two hundred yards," said Quadros, pointing. He eyed the watch she held out but refused to touch it.

Perhaps he thought Pangborn's death was contagious. Another primitive superstition... Katherine stopped herself in mid thought. If she had learned one thing from this trip it was that it didn't pay to dismiss what the Indians said. After all, they had been right about the mapinguari, hadn't they? But there was time enough to explore Quadros's feelings about the watch later. Right now, it was probably wise to put as much mileage between the mapinguari and themselves as possible.

"Let's get out of here, Quadros," she said fervently, putting the watch safely in her breast pocket. "I've had enough of this place to last me a lifetime, and we must report Pangborn's death to the authorities - though they're never going to believe what happened."

"You'd be surprised what they'll believe, senhora."

She remembered the video camera and laughed a little hysterically. "At least we're not going back totally empty handed. I can't wait to see Collier's face when I show him the mylodont footage."

"I too would enjoy seeing that, senhora." Quadros helped her on with her pack. "Okay. Let's go." And they set off on the long journey back to Manaus.