The snarls and grunts of the infected changed pitch, suddenly becoming more urgent, more eager. Then they heard Purna's rapidly approaching footsteps, in the wake of which came the bestial clamour of pursuit. The footsteps grew louder, reaching a crescendo as Purna clattered up the steps. She burst through the doorway, almost slipping in West's blood before regaining her balance.

'They're right ... behind me ...' she gasped.

She had barely made it out of the line of fire before the infected were spilling into the room. As soon as they appeared, Logan, Sam and Xian Mei started firing, cutting down men, women and children alike. Blood, flesh and bone flew everywhere. In less than a minute the doorway was clogged with bodies. Yet still the infected came, uncaringly clambering over their fallen comrades, stamping on their faces and slipping in their blood, in their desperate desire for warm, living meat.

As the firing continued and the last of the infected collapsed on top of the tangle of once-human bodies, so the wave of blood leaking and spurting from dozens of wounds and ruptures fanned out across the floor. Grimly Logan, Sam and Xian Mei continued to stand their ground as the blood tide lapped against their boots, oozing around them like something alive.

Finally, however, it was over, and the guns fell silent. Sam, enervated, felt his arms droop to his sides, that sense of numbness, of unreality, of faint self-loathing creeping over him again. He shuddered, shaking it off, and stepped backwards out of the blood, the soles of his boots making a sticky squelching sound as he did so. From what seemed like the bowels of the earth, Yerema's voice called out, 'What's happening up there?'

Sam tried to reply, but for a second his voice wouldn't come. It was Purna who answered, 'We're all OK.'

'What about the infected?' asked Yerema.

Purna hesitated, as if searching for some way of describing what had happened without making it sound as ugly and brutal as it had been. Finally, however, she simply said, 'They're dead. We got them all.'

'So I'm the last then,' said Yerema, a hint of disbelief creeping into her voice. 'The last of the Kuruni.'

For the next few minutes the four of them occupied themselves with the grim task of dragging aside the sprawled and mangled bodies blocking the doorway. No one spoke, and by the time they were done their hands were gloved in red and their clothes were once again stained and stinking with zombie blood.

Though Yerema was grateful to be rescued and hugged each of them in turn, she was not jubilant, recognizing that theirs was a hollow victory.

'So what happened?' asked Purna.

Yerema shook her head. 'It was one of the guards. A Kuruni child was sick, having seizures, so he opened the cage. Either he hadn't been fully informed about the virus or he simply didn't appreciate how dangerous it was. Anyway, he was attacked and the infected got free. I guess the other guards must have been reluctant to use their guns at first they probably thought the infected would respond to threats. By the time they realized their mistake, it would have been too late.'

'But you were smart enough to lock yourself in one of the cages,' said Xian Mei.

To their surprise Yerema shook her head. 'I didn't lock myself in,' she said. 'Dr West locked me in earlier.'

'West?' exclaimed Logan. 'Why?'

'He wanted to use me as a guinea pig, give me a shot of the vaccine he had developed to see how it affected the dormant virus in my system. But I didn't want him to. I thought it was too dangerous. He'd admitted earlier that if he didn't get it right the vaccine could have the opposite effect and kick-start the virus into fighting back. He tried to inject me by force, but I knocked the hypodermic out of his hand and stamped on it. So he dragged me down to the cells and locked me in, telling me that once he'd prepared another hypodermic he'd be back. But a few minutes later the guard arrived to feed the prisoners and made the mistake of opening the cage, and that's when everything started to go wrong. The infected got out and killed everyone and then they came back for me. I didn't know what had happened to West until now. Despite everything, I was kind of hoping he'd managed to get away.'

'So he did develop a working vaccine before he died?' said Purna.

'That's what he told me. But I don't know how safe or effective it was. I know he hadn't properly tested it.'

'Even so, it's the best we've got,' said Purna, looking around the laboratory. There was plenty of equipment still intact on the work surfaces, but nothing that jumped out at her, nothing obvious.

'So where is it?' she asked.

Yerema shook her head. 'I've no idea.'

'We've got to find it,' said Purna firmly. 'We can't leave until we do.'

Chapter 20.

ENEMY MINE.

'GO TO THE left.'

Xian Mei relayed the instruction to Mowen as the hand-held mine detector, not much bigger than a TV remote control, began to beep insistently. The detector consisted of a mostly black display screen, which depicted Mowen's boat as a slowly moving white dot. Whenever they got close to one of the hidden underwater mines surrounding the prison island, a flashing red dot would appear, accompanied by a high-pitched beep. The closer they were to the mine, the more frantic both the flashing and the beeping would become. Mowen had told them that he sometimes ran errands for the prison governor and had been given the device to enable him to move safely through the waters between Banoi and the smaller island a couple of miles offshore. He didn't elaborate on the nature of the errands, and no one asked.

Because they had to be almost on top of a mine before the detector picked up its signal, progress through the water was slow. For a while it seemed that the black island jutting from the sea, dominated by its forbidding grey tower like the domain of an evil sorcerer in a fairy story, wasn't getting any closer. Not that Sam, for one, minded at all. Despite their destination, he was just glad to be heading away from Banoi and to be breathing fresh air untainted by the stench of corruption. It was a glorious day, the eggshell-blue of the sky reflected in the deeper blue of the calm and glittering ocean. Odd to think that, like Banoi itself, the sea's beauty concealed such deadly danger lurking beneath its surface.

Inevitably, however, they did eventually draw closer to the island, the jagged black rocks that fringed the shoreline like the beckoning claws of some vast leviathan. The island itself, which rose to a plateau on which the prison was built, appeared to swell from the ocean. As Mowen slowly and skilfully steered his boat through the rocks towards a small inlet, Purna dialled Ryder White's number.

'We're here,' she said when her call was answered. 'How do we get in?'

Reception was poor, a mass of white noise through which White's voice could barely be heard. 'Climb over elec ... fence. I'll cut off ... tricity supply for an hour once you're up on the plateau ... give you chance to-'

A prolonged burst of static drowned out his next words. Purna winced and held the phone away from her ear. 'I'm losing you, White,' she shouted. 'What did you say?'

For a moment there was simply more white noise, then it died away a little and Purna heard White's voice, faint and distorted, rising up through it again.

'... make for Sector Seven. I repeat, Sector Seven. But be care ... fected everywhere.'

'Got it,' said Purna. 'See you soon.'

She rang off and told the others what White had said. They drifted into shore and Mowen cut the engine. Before them, clear water lapped gently at a stony, sloping beach. Beyond that rose a gentle cliff face, levelling out to the plateau perhaps thirty metres above. Ringing the plateau was a four-metre-tall security fence topped with metal spikes. Signs at five-metre intervals depicted a skull beneath a zig-zagging lightning bolt, white on red. Though the fence was high above them, they could hear it humming faintly, and through it they could just make out vague dark shapes wandering aimlessly about the infected with nothing to attack.

Purna sighed. Her life seemed to have boiled down to little more than a succession of obstacles, and here were more of them. She looked at her fellow survivors a patched-up, motley bunch of strangers, who in the past couple of days had been through hell, both collectively and individually, and who had been forced to mould themselves into a ruthless fighting unit in order to stay alive. She fervently hoped that their ordeal was now, finally, coming to an end, that soon they would be able to return to their old lives and (as much as they were able) put this terrible episode behind them. However, in her heart of hearts she suspected that the outcome would not be quite as simple and straight forward as that, and that even if everything did eventually work out, there were still battles ahead to be fought and won.

They disembarked, each of them carrying a weapon and a backpack of provisions. She, Sam, Logan and Xian Mei still had the assault rifles they had liberated from the police station and in whose use they had become reasonably proficient over the past couple of days. The younger girls, Jin and Yerema, each carried Smith and Wesson semi-automatic pistols. Since her terrible ordeal in the police station, Jin had abandoned her pacifist principles and seemed to have accepted that the only way she would survive was to arm herself and be prepared to fight. Although Purna was glad the girl's attitude had changed, she wouldn't have wished the cause of it on her worst enemy, and even now she kept going over and over the episode in her mind, wishing she had made better decisions.

Once they were ashore, Mowen raised a hand in farewell. 'I go now.'

Logan stepped forward and shook the trader's hand. 'Take it easy, man,' he said. 'Thanks for everything.'

Mowen nodded, implacable as ever, his eyes still hidden behind his shades. 'Good luck,' he said.

'You too,' said Sam, also shaking Mowen's hand, while Xian Mei, Jin and Yerema smiled and nodded in agreement. Purna, however, simply gave a single curt nod, acknowledging Mowen's help, but knowing that the relationship between themselves and the trader was fragile and temporary at best. It was based on Mowen's part not on mutual respect and a genuine willingness to help, but purely on monetary gain.

They watched Mowen's boat chug slowly away, then they turned back to the matter at hand. Purna led the way, as she so often did, as they trudged towards the gently sloping cliff face and began to climb.

It was neither a long nor particularly arduous journey to the summit, but the heat of the sun and the weight of their backpacks were more than enough to sap their strength. By the time they reached the plateau they were each panting and sweating and grateful for a drink. As they sipped water and looked through the buzzing electric fence at the drearily ominous prison building across the two-hundred-metre square expanse of a flat and dusty exercise yard, those infected who had been milling outside began based on their physical ability to shamble or run or crawl towards them.

'Here we go again,' Sam said almost wearily and unshouldered his rifle. At the same moment the low humming of the electric fence ceased.

'White's turned it off. That gives us an hour,' said Purna.

'How did he know we were here?' asked Jin.

Purna pointed silently up at one of many CCTV cameras mounted high enough on the prison walls that they couldn't be damaged or disabled. A second later the first of the infected threw himself against the security fence with a metallic crash.

He was a big shaven-headed man with a rearing cobra tattoo on the side of his neck. Like most of the zombies here, he was wearing orange prison overalls. To everyone's surprise it was Yerema who raised her pistol and shot the man in the head. He fell like a sack of cement, face turning slack and almost baby-like as the savagery abruptly went out of him.

'You done that before?' Purna asked, regarding the girl shrewdly.

Yerema shook her head, trying not to look shocked at her own actions. 'No, but I knew that to survive I was going to have to kill. And I also knew that the more I put it off the harder it would be.'

Purna nodded in grim approval and tried not to flash a knowing look at Jin.

'If it helps, try not to think of it as killing,' said Sam. 'Try to think of it as switching off a dangerous machine. Whoever that guy was, he died a while ago. All you've done is stopped the virus from using his body.'

Yerema nodded her thanks as more of the infected hurled themselves against the security fence. They rammed their faces between the bars, growling and snapping like vicious but frustrated guard dogs.

No one needed to be told that the creatures would have to be dealt with before the six of them could even think of climbing the fence into the prison. Like kids at a shooting gallery, they silently arranged themselves into a line, raised their guns and began to pick off the infected one by one.

There were around sixty of them, maybe more, but it was over in a matter of minutes. As soon as the last of the infected had fallen, Purna, Sam and the rest lowered their weapons and moved further along the fence, stopping at a spot far enough away from the carnage that they wouldn't be trying to avoid landing in the spreading pool of blood when they climbed over.

Purna went first, scaling the fence with ease, then Sam and Logan gave the other three girls a leg up before tackling the barrier themselves. Both men gritted their teeth as the effort of climbing stretched and tensed the muscles in their arms and legs, making their various bites Logan's in his shoulder, Sam's in his calf throb with pain. However, each spurred on by the other's determination, they eventually made it over.

As soon as they began to hurry across the open ground towards the prison building, a chorus of different sounds erupted into life. For one crazy moment Sam thought they had set off some kind of alarm, then he realized the noise was coming from them, and was the combined ringtones of their cell phones.

'What the fuck?' said Logan, looking down at his pocket as if a scorpion had just crawled out of it.

Purna, however, already had her cell phone in her hand. 'Yep?' she snapped without breaking stride.

The others could hear nothing but the crackle of white noise and the hint of a tinny voice.

'OK, thanks,' Purna said before breaking the connection and slipping the phone back into her pocket.

'White?' guessed Sam.

Purna nodded.

'What did he say?' Xian Mei asked.

'He said to move to our left and that the first door we come to should be entrance number 4. Once we're there he'll unlock it for us.'

Sam glanced up and around. 'I don't like the thought of being watched,' he said. 'It gives me the creeps.'

'If it makes our task easier then personally I'm all for it,' said Purna.

They moved quickly across to the building and followed the line of the wall until they came to an alcove that resembled a short, high-sided alleyway. At the end of the alleyway was a grey metal door with a black number 4 stencilled on it, mounted above which was a security camera in a protective cage. As soon as they came within sight of the camera, a series of hefty chunking sounds suggested that several heavy-duty locks were being disengaged. With barely a glance at the overhead camera, Purna moved to the door, shoved down the handle and pushed.

It groaned open slowly and heavily like the door of a bank vault. Beyond was a short featureless corridor, the floor made of some black vinyl-like substance, the bare stone walls painted an institutional cream. At the end of this corridor was another metal door with another security camera mounted above it. Again there was a series of heavy chunking sounds.

'Open sesame,' murmured Sam.

'Anyone else get the feeling this is almost too easy?' asked Logan.

Purna shot him a stern look. 'Don't get complacent. White said the place was swarming with the infected.'

'I'm suspicious, not complacent,' said Logan.

'The man's only helping us because he's desperate for the vaccine,' said Xian Mei.

At the back of the group, Yerema called, 'Shall we close the outside door or leave it open?'

Purna considered a moment, then said, 'Leave it open. It makes us more vulnerable to attack, but on balance I'd rather have an escape route.'

Cautiously she opened the second door. Beyond was a large dining room, containing ugly, functional rows of tables and chairs that had been bolted to the floor. Along the left-hand wall was a line of stainless-steel serving units, which at meal times no doubt contained tin trays of gristly meat, overcooked vegetables and sloppy mashed potatoes or whatever the Banoi prison equivalent was.

All was quiet here too, though on the far side of the room were two sets of barred metal doors, beyond which could faintly be heard an uncoordinated chorus of echoing thumps and clangs accompanied by low groans.

'Happy now?' Purna said to Logan as the two of them moved cautiously across the room.

'Delirious,' muttered Logan.

'Let's call White,' said Sam, 'see what we're-'

Before he could finish his sentence, one of the girls behind him screamed. He, Logan and Purna spun round, guns jerking up instinctively. Xian Mei too was turning to face the door through which they had entered, as was Yerema. What they saw was Jin, who had fallen back to the rear of the group, and a black-bearded man in prison overalls. With his left hand the man had twisted Jin's arms behind her back, causing her to drop her gun, and was now holding her in front of him like a human shield. In his right hand he held a large and very sharp-looking carving knife, the blade pressed against Jin's throat.

'Hey!' Sam shouted angrily and started forward, but halted when the man simply tightened his grip on Jin. At the same time he nicked the skin of her throat just enough to draw both blood and a high-pitched sob of terror from her. Purna raised a hand to indicate that everyone, including the man himself, should stay calm.

The prisoner licked his lips and grinned nastily, clearly relishing the fact that despite being armed with nothing more than a knife he was fully in charge of this situation.

'Drop your fucking guns and back off,' he sneered, 'or I'll cut your friend open like a fucking pig.'

Chapter 21.

HOSTAGE SITUATION.