'It's nearly full,' she said, calmly. 'It'll drop off soon.'

'Take if off now!' demanded Amber.

'I can't do that,' said Li. 'We need some heat or alcohol or something to make it let go. If I try to pull it, the head will come off and the jaws will be stuck in your leg. Then it'll get infected and-'

'I want it off now,' moaned Amber.

'Hey! It's your fault we're up to our knees in a mangrove swamp!' snapped Li. 'You're the one who insisted we came back this way!'

She turned away from Amber and pushed her long, black hair away from her sweaty face, trying to figure out when things had started to turn sour. The first part of the morning had gone well. They had worked their way around the coastline until they came to the mangrove swamp. Then they had headed inland, following a game trail and stopping to gather ripe, orange pawpaws and wild figs on the way. The game trail had taken them neatly around the swamp to the base of the headland. From there, it had been mainly hard, uphill walking, with one final, short section of real climbing, which Li had managed easily. Once she reached the top, Li had anchored the nylon line to a rock outcrop and lowered the other end for Amber to tie around her waist with a bowline. To Li's surprise, Amber had climbed slowly but well, following her route almost exactly. Li made sure she kept taking in the rope as Amber climbed, keeping it taut just in case, but it was never really needed.

At the top of the headland, they had discovered a tiny, fresh-water run-off, where they filled the plastic bottle to take back with them. Then they had found a rock to lean against as they rested together, sharing the can of lemonade and looking out to sea. They had scanned the sea again and again but saw only featureless water, stretching to the far horizon. There were no planes, no ships and no other islands.

Discouraged, they had turned their backs on the sea to study the geography of this side of the island. Below and to the east was their lagoon, with the reef beyond. It was the only stretch of sand in sight. The rest of the coastline was a hostile mixture of mangrove swamps and rocky headlands. Behind them the rainforest stretched like a huge green, moving sea and above them the mountain climbed skyward. Li studied the shape and contours of the island for a long time. Finally, she sat back, satisfied that she had worked out and memorized the best route round to the other side of the mountain.

'Looks like we're on our own,' she said, looking out to sea again. 'The Phoenix could be anywhere out there.'

'But they must be missing us by now!' protested Amber.

'They may be missing us, but that doesn't mean they know where to find us,' Li had replied. 'They don't know about the current. They don't know we lost an oar. They have to search the most obvious places first. Today, they'll double back and search yesterday's route.'

That was when things had started to go wrong. Amber had turned sullen and difficult on the way back and had insisted that she did not have the energy to walk much further, so against Li's better judgement they had cut through the swamp instead of going round it.

Now Li snorted as she squatted next to Amber on the roots of the mangrove tree. 'Some short cut this turned out to be,' she said, swatting a persistent mosquito.

Amber was talking to herself in a trembling monotone. 'I can't believe it. Ten days ago I was sitting in the Savoy, having afternoon tea with my uncle. I was wearing a Prada dress and a pair of simple, diamond earrings. We shared a pot of Earl Grey and talked about buying a house in London. Now, I'm in the middle of a swamp, covered in mosquito bites with a leech hanging off my leg!'

Li hid a smile and turned back to the problem of the leech. 'You're wrong about one thing,' she said, looking at the back of Amber's knee. 'You don't have a leech hanging off your leg. It finished its lunch and left quietly, just like I said it would. See?'

Amber twisted to look at the back of her knee, then gave Li a weak smile. 'Sorry about the swamp,' she said. 'I was so tired and I thought it would be quicker. I was wrong.'

Li glanced at Amber in surprise. She did look exhausted. Her face was covered in a sheen of sweat and the skin around her mouth had an unhealthy grey tinge to it. 'Come on,' said Li, softly. 'We're nearly through it, see?' She pointed to the green dome of the rainforest, rising above the swamp. 'We can pick up the game trail again just over there-'

Li stopped in mid-sentence as a series of hisses and deep, grunting roars came out of the rainforest and travelled clearly across the still waters of the swamp. An explosion of brightly coloured birds shot out of the top of the rainforest canopy and the undergrowth shook as something big thrashed and crashed about amongst the trees.

'What is that?' whispered Amber.

'I'm not sure,' said Li, gazing at the fringes of the rainforest. 'But I have a feeling it wasn't such a mistake coming back through the swamp after all.'

'Why?'

'Because if we'd gone around the edge of it again, we would've met – whatever that is.'

Amber stared over at the threshing undergrowth and listened to the hissing roars. 'Trouble is, we have to go back into the forest at some time,' she said, in a wobbly voice. 'It's the only way back to the beach.'

ELEVEN

'Alex. It is time to head back.'

Reluctantly, Alex came to a stop in the middle of the game trail.

'We have walked for ten minutes,' said Paulo, tapping his watch. 'We must be back on the beach at the rendezvous time,'

Alex nodded but stayed where he was. He did not want to retrace his steps when a stream of fresh, gurgling water could be waiting for them just around the next bend. He put a hand to his aching head, trying to decide whether to keep walking for another five minutes.

Paulo waited patiently for Alex to make up his mind, letting the peace of the primary rainforest settle around him. The trees were massive here, with huge trunks supporting a high, green canopy of leaves so dense that the sun could not break through. Under the canopy, it was cool and dim, and there was a constant background noise made up of the singing of crickets and birds, the rustle of leaves and the tiny scrabblings of millions of insects. Paulo tilted his head, listening. The forest sounded busy, purposeful. He smiled. It reminded him of the hum of a huge piece of machinery, and he liked machines. Suddenly, his head came up and his eyes widened as he realized he was hearing a new noise.

'Listen,' he hissed.

Alex tensed and raised his stick, then he saw the look of sheer delight on Paulo's face.

'I hear water,' said Paulo.

They ran, dodging low branches and swinging vines. The trail was climbing steeply now and the light grew stronger as the canopy thinned above them. They burst out of the forest into a clearing at the base of a rock outcrop on the lower slopes of the mountain. Alex and Paulo stumbled to a halt and stared. Directly ahead of them, water poured from a hole in the face of the rock, cascading down to a shallow pool which had been hollowed out of the ground beneath.

Alex unclipped the pouch from his belt and dropped it next to their sticks and the rucksack, then they both ran into the pool, fully dressed and still in their boots. The water was cold, clear and refreshing after its journey down through the centre of the mountain.

'Don't drink any,' warned Alex, as Paulo plunged straight under the waterfall. He stood there, whooping and yelling as the water washed away the sticky layers of salt, sweat and blood. Alex stayed in the quieter waters, grinning with relief because they had finally found their fresh water supply. He studied the area, looking for signs that the water was good. There were plants and vines hanging from the outcrop around the waterfall and the rocks were covered with bright green mosses. The vegetation around the pool was cropped short and there were many hoofprints in the wet clay edging the water.