Tunnels

snarling and barking and voices were closing around him. He lost his nerve and simply slung the firecracker to the ground.

'Will, Will!' he heard up ahead. As he homed in on the shouts, he was furious that Cal was making so much noise, though he knew he would never have found him otherwise. Will was running at full tilt when he caught up with his brother and almost bowled him over. They were sprinting furiously as the first firework went off. It screamed out in all directions, its bright primary colors bleeding through the texture of the fog before it ended with two deafening thunderclaps.

'Keep going,' Will hissed at Cal, who had crashed headfirst into a wall and was acting a little stunned. 'Come on. This way!' he said, pulling his brother by the arm, not allowing him any time to dwell on his injury.

The fireworks continued, exploding fireballs of light high into the cavern or in low arcs that ended in the city itself, momentarily silhouetting the buildings like the scenery in a shadow play. Each iridescent streak culminated in a dazzling flash and a cannon-shot explosion, echoing and rumbling back and forth through the city like a raging storm.

Every so often, Will stopped to light another firecracker, picking out Roman candles, air bombs, or rockets, which he positioned on pieces of masonry or threw to the ground in the hope of confusing the patrol as to their position. The Styx, if they were still following, would be bearing the brunt of this onslaught, and Will hoped that at the very least the smell of the smoke might put the stalker off their scent.

As the last of the fireworks exploded in a cavalcade of light and sound, Will was praying he'd bought them enough time to reach the Labyrinth. They slowed to a jog to allow themselves to catch their breath, then stopped altogether to listen out for any sign of their pursuers, but there was nothing now. They appeared to have shaken them off. Will sat down on a wide step of a building that looked like it could have been a temple and took out his map and compass while Cal kept watch.

'I've no idea where we are,' he admitted, tucking the map away. 'It's hopeless!'

'We could be anywhere,' Cal agreed.

Will stood up, looking left and right. 'I say we carry on in the same direction.'

Cal nodded. 'But what if we end up right back where we started?'

'Doesn't matter. We've just got to keep moving,' Will said as he set off.

Once again the silence crowded in on them, and the mysterious shapes and shadows appeared and softened as if the buildings were pulling in and out of focus in this invisible city. They'd made tortuously slow progress through a succession of streets when Cal came to a standstill.

'I think it's clearing a little, you know,' he whispered.

'Well, that's something,' Will replied.

Once again Bartleby stiffened and crouched down low, hissing as the margins of the fog rolled back before them. The boys froze, their eyes feverishly raking the milky air.

As if veils were being lifted to reveal it, there, not twenty feet away, a dark, shadowy form was hunched menacingly. They both heard a low, guttural growl.

'A stalker!' Cal gulped.

Their hearts stopped with awful realization. They could only watch as it rose up, its muscular forelegs tensing into life as it pawed the ground, then began to move, accelerating forward at a bewildering speed. There was absolutely nothing they could do. There was no point in running; it was too close. Like an infernal steam engine, the black hound was pounding toward them, condensation spewing from its flaring nostrils.

Will didn't have time to think. As he saw the dog spring, he dropped his backpack and shoved Cal out of the way.

The stalker soared through the air and slammed heavily against Will's chest. Its clublike paws knocked him flat on his back, his head thwacking the algae-covered ground with a hard slap. Half stunned, Will reached up and grasped the monster's throat with both hands. His fingers found its thick collar and hung on to it as he tried to hold the brute away from his face.

But the animal was just too powerful. Its jaws snapped at his mask, then caught on to it and bit down. Will heard the squeal of its fangs tightening on the rubber as the mask was crushed against his face, and then a pop as one of the eyepieces shattered. He smelled the putrid breath of the stalker, like warm, sour meat, as the animal continued to wrench and twist the mask, the straps behind Will's head stretched almost to the breaking point.

Praying the mask would stay in place, he tried with all his might to turn his head away. The stalker's jaws slid off the wet rubber, but Will's success was short-lived. The dog pulled back slightly, then immediately lunged again. Screaming, and still hanging on to its thick collar with all his might, Will was barely managing to keep it away from his face, his arms at the very limit of their strength. The collar was cutting into his fingers — he couldn't believe how heavy the beast was. Time after time, Will whipped his head away, only just evading the snapping teeth, like the jaws of a powerful trap clapping shut.

Then the animal contorted and twisted its body.

One of Will's hands lost its grip, and with nothing to hinder it the animal quickly sought out a more rewarding target. It caught hold of Will's forearm and bit down hard. Will cried out from the pain, his other hand involuntarily opening and letting go of the collar.

There was nothing to stop it now.

The animal instantly scrabbled over him and sank its incisors into his shoulder. Amid the growling and biting he heard the cloth of his jacket rip as the huge teeth, like twin rows of daggers, penetrated and tore into his flesh. Will wailed again as the animal shook its head, snarling loudly. He was helpless, a rag doll being shaken this way and that. With his free arm, he punched weakly at the animal's flanks and head, but it was no use.

Then suddenly the dog detached itself from his shoulder and reared up over him, its huge weight still pinning him down. As its frenzied eyes fixed on his, he could see its slathering jaws just inches from his face, strings of its drool dripping into his eyepieces. Will was aware that Cal was doing all he could to help; he was quickly lunging in to pummel and kick at the beast, then just as quickly pulling back. Each time he did this, the dog merely half turned to snarl at him, as if it knew Cal posed no threat. Its small, savage brain was fixed on only one thing; the kill that was completely and utterly at its mercy.

Will tried desperately to roll over, but the creature had him pinned to the floor. He knew he was no match for this unstoppable hellhound that seemed to be made from huge slabs of muscle as hard and unyielding as rock.

'Go!' he yelled at Cal. 'Get away!'

Then, from out of nowhere, a fleshy bolt of gray catapulted a the stalker's head.

For one instant, it was as though Bartleby was suspended in midair, his back arched over and his claws extended like cutthroat razors just above the stalker's head. The next, he'd dropped, and there was a shocking frenzy of movement. They heard the wet slicing of flesh as Bartleby's teeth found their first mark. A dark fountain of blood was jetting over Will from a livid gash where the dog's ear had been. The beast let out a low-pitched yelp and immediately bucked and leaped off Will, Bartleby still clamped to its head and neck, blitzing it with bites and savage flesh-tearing slashes from his raking hind feet.

'Get up! Get up!' Cal was shouting as he helped Will to his feet with one hand and retrieved his backpack with the other.

The boys retreated to a safe distance, then stopped, compelled to stay and watch. They were rooted to the spot, transfixed by this brute battle between cat and dog as both writhed in mortal combat, their shapes melting together until they became an indistinguishable whirlwind of gray and red, punctuated by flashing teeth and claws.

'We can't stay here!' Will yelled. He could hear the shouts of the approaching patrol, which was quickly homing in on the fight.

'Bart, leave it! C'mere, boy!'

'The Styx.' Will shook his brother. 'We have to go!'

Cal reluctantly moved on, peering back to see if his cat was following through the mist. But there was no sign of Bartleby, only the distant hisses and yelps and screeches.

Shouts and footfalls were now echoing all around. The boys ran blindly, Cal grunting with the effort of carrying both packs, and Will trembling with shock, his whole arm throbbing dully with pain. He could feel the blood streaming down his side and was alarmed to find that it was running over the back of his hand in small rivulets and dripping from the ends of his fingertips.

Out of breath, the boys hastily agreed on a direction, hoping against hope it would take them out of the city