For a moment Darien just stood there, staying absolutely still. There was no way he'd imagined it. The very rock beneath him had shifted, but it hadn't been the violent tremor of a quake. The motion was too smooth for that. He looked at Hekket.

"You felt that...right?"

His companion nodded, a look of apprehension stamped on his face. Slowly Hekket stood up, edging away from the spot where he'd taken a sample. The ground moved again in an almost gentle motion, and the deep bass note again throbbed agonizingly in their ears. Clenching his jaw tight against the pain, Darien concentrated on keeping his feet. A grinding sound reverberated through the water as whatever it was scraped against the walls of the Coring Well.

Something was very, very wrong.

He could see more expulsions of bubbling water coming out of the crack he'd been examining. They were coming more regularly now, increasing in tempo, and he could feel the faint tug of the current even from several meters away.

"Darien..."

Hekket's hoarse gasp made him swing back to look. The other boy was staring with a look of horror at the spot where the sample had been cored from. Following his gaze, Darien was shocked to see a strange, oily fluid seeping in wisps from the incision, weaving up through the dark water like a phantom.

"What's happening?"

"That's not rock."

"Then what..."

His voice trailed off at the sound of a low muffled rumble in the water. He looked up into the darkness that they'd passed through just minutes before. He couldn't see anything definite, but the water was moving, shaking.

"Hekket," he said quietly. "Get off the surface. Follow me."

Kicking the micro-jets into gear he propelled himself up off the slowly rotating surface and started swimming, a horrible feeling taking root in the back of his mind. He prayed that his guess would be wrong. But then a lump of stone the size of his torso sank past him and his heart sank with it. He cast the beam of his torch through the dark, towards the place where the collapsed pillar had been. He suspected that if the surface they'd been standing on wasn't rock, then that support was not a support at all.

Sure enough, his blood turned to ice at the sight that met his eyes.

What they'd thought was a pillar was currently being pulled from where it had been driven into the wall, and its segments bent in a motion that was horrendously life-like. Slowly, inexorably, it retracted, pulling lumps of debris from the wall as it moved.

"Impossible."

"That's not a support strut," Darien gasped. "It's a leg."

"That message – the warning – and all those carvings." Hekket didn't sound calm anymore. He sounded utterly shocked. "You don't think...the Leviathan that alien talked about, could this be...?" It was almost like he didn't want to finish the sentence, letting his voice fade out into a numb silence.

Darien braced himself for the worst and looked down.

As a Blink Operative, Darien Flint had seen a lot of strange and frightening things, but nothing even approached the dumbstruck horror that gripped him when he found himself staring down at the Leviathan of Marianas. The head alone was dozens of meters across and eyes as wide as he was tall stared into the gloom. A jaw that could have swallowed a house hung open, bubbling and frothing as the water around it churned, and it was filled with two matching rows of fangs. The head also sported two scarred, grey tusks, each one as long as a truck.

For a moment he just floated there, stunned, not quite believing what he was looking at. The thing's sheer mass stretched beyond the lights of the glow nodes, vanishing into the blackness, but as it rotated he could see other limbs coming into view, pulling free from the walls. It was like watching a mountain come to life. On its cragged carapace the marks he'd mistaken for crevices were spewing water in and out like enormous gills.

Although he couldn't see all of it he knew it had to be big enough to block the entire Coring Well. That made it at least two hundred meters across, possibly more. He saw, to his further horror, smaller creatures come creeping out of the cracks in its outer shell, summoned from their slumber as their vast host awoke. At this distance they looked tiny compared to the Leviathan itself, but Darien's mind still recognised the scale. Each one was easily several meters long.

Everything fell into place like the world's most terrible jigsaw puzzle. This was what had forced the alien residents to flee their home. This monstrous, titan of the depths that by all natural laws was so colossal it shouldn't even exist, along with its army of parasites. The strange circular wounds they'd observed in the dead aliens were fang or tusk marks from the smaller creatures. The thought shook him even further.

The two stunned teenagers stared for several long seconds as the Leviathan shook itself ponderously into life, sending cracks shivering up the walls of the Coring Well as its movement become more violent. Then the water around its cavernous mouth seemed to shake and the terrible bass note rang out through the water again, like a whale song written by the devil.

Hekket spoke first.

"What the fu-"

"Surface!" Darien shrieked. "NOW!"

The panic in his voice galvanised his companion into action and together they turned, drove their micro-jets up to maximum and ploughed upwards through the water, away from the impossible creature below. All Darien could think of was getting out of the water, out of the Coring Well, and out of the city. Nothing and no-one on the planet was ready to deal with what they'd just discovered.

"Darien, what in the hell did you two do down there?!" Idas's voice suddenly burst out of his earpiece. "The Coring Well is shaking itself to pieces-" he broke off for a moment and a resounding crash sounded in Darien's earpiece. "The wreckage is getting tossed around and so am I! We need to get out of here."

"I'm pretty sure we just woke up the Leviathan," Darien replied simply, unable to think of anything more substantial. "Hang tight, we're on our way!"

"Wait...WHAT?!"

"Just hold on! We're coming!"

There was no point trying to explain, especially not right now. He could still hear the deep bass call of the Leviathan booming through the water around them and more cracks were beginning to appear in the walls as it dragged itself back to life. Darien had no way of knowing how long it had been motionless down there, a titanic sentinel guarding this cold, dead world, but it had almost become part of the superstructure. Now that it was moving once more the effects were going to be catastrophic.

The shaking surface of the Coring Well rushed up to meet them with a welcome suddenness, and Darien tucked his limbs close to his body, forming as aerodynamic a shape as he could to aid his flight. The tether remained slack – Hekket must have been at least matching his speed. He didn't dare look back.

When he finally broke the surface he looked around for Idas. What he saw was the huge structure of one of the stranded submersibles careering towards him, its huge hull crashing against the ground as it was shaken into motion. He immediately dived again as the brazen wreck smashed against the edge of well.

It plunged into the water but he was already in motion to avoid it, hurtling underneath the carcass as it broke the surface. He felt the tether catch for just a second before his companion followed his path. Once again he surfaced, coming up on the other side of the wrecked submersible and clambering his way up one of the huge ramps that ringed the Coring Well. Spinning, he took a hold of the tether, ready to pull if he had to.

Hekket exploded from the water a few meters behind him, eyes wide as he dragged the breather mask from his face without breaking stride. Without a word he unclipped the tether and tossed it to Darien.

"Idas!" Darien roared above the thunder of breaking masonry and crashing wrecks.

"Over here!" the bullish voice of his friend rose over the clamour. He looked around frantically for the source, and spotted Idas over near one of the entrances. The other boy beckoned wildly. "Come on, we can get clear this way!"

"You heard him," he snapped, glancing back at Hekket. "Let's move it!"

Then it was time to run the gauntlet. Between them and the nearest exit more of the ancient wrecks were being thrown around by the tremendous shaking, and huge cracks had started to appear in the floor and walls. Even the massively reinforced structure of the Coring Well couldn't withstand the titanic forces now being unleashed beneath them.

Another of piece of wreckage smashed and rolled its way past them, shedding bits of metal as it went. With Hekket close behind, Darien let the way into the maelstrom, sprinting flat out in a zigzag line around the larger hunks of debris. He had to duck as one of the alien corpses was flung toward him by a particularly violent buck of the ground. Then without warning the floor in front of him split open just as he was making a stride. Unable to stop his forward momentum he tried to jump the rising ledge of concrete, but his right boot caught the edge, launching him head over heels forward.

Darien hit the ground with a growl of pain and frustration, struggling to get back to his feet as the room continued to shake. Then someone took a grip of the back of his combat vest and dragged him scrambling to his feet.

"You alright?" Hekket shouted over the noise as they pelted side by side through the mayhem.

"Fine, just scrapes," he called back. Getting his bearings, he spotted Idas, much closer now and still beckoning wildly. Beside him was something that looked like an old fashioned garbage skip – a large rectangular box around ten feet in length.

Then a rending crack echoed through the chamber and Darien looked up, a sick feeling settling in his stomach. Above them a long dark wound had broken in the thick ceiling of the Coring Well, and through it the ocean had started to pour.

"You've got to be kidding," Hekket gasped.

Darien shoved him forward. "No such luck. MOVE IT!"

A veritable waterfall cascaded into the gigantic dome, although against the mass of the whole structure the crack was relatively small. With the sea smashing against the stone behind them, Darien hurtled onward, ducking, dodging and dancing his way through the obstacles of the Well. Eventually they reached Idas at the exit and he turned his eyes on the strange box-like contraption.

"Okay, Idas, we're here," he said. "What the hell is this?"

"It's some kind of rail carriage," Idas replied. "It runs along those gravity discs like the elevator, only it goes along the ground instead of going up. Way I figure it's our quickest way away from..."

"I'll explain on the way." Darien didn't bother asking any more questions. He simply cupped his hands and nodded to Idas. "I'll give you a boost."

With the sound of the Coring Well being shaken to pieces still ringing in their ears, the operatives didn't waste any time. A moment later the three of them stood inside the alien carriage and Darien positioned himself at the main controls at the front. He couldn't see the corridor anymore – the walls of the carriage rose up too high for that.

"If this is anything like the elevators we're in for a wild ride," he warned. "So brace yourselves." While his companions positioned themselves at the rear of the carriage, tucked into the corners against the inevitable jolt, Darien wrapped his climbing tether tight around the main control console. The map display was similar to the elevator, but presumably this one was horizontal. After taking a moment to examine it, he picked his spot, took a tight hold of the tether and pressed the light.

He felt the surge as the carriage shot into motion, but this time with the tether he only wobbled under the onslaught. The map display pulsed with their position as they careened through the city depths.

Then the carriage struck something. Something big.

None of them had time to react as the carriage slammed into the obstruction at full speed. There was a sickening crunching sound and what sounded like a hissing screech – then the carriage derailed. Darien could only cling onto the tether and pray as their transport rebounded off the walls at a terrifying speed, crashing and banging like an enormous pinball. Miraculously, it didn't tip over, its heavy wide base being enough to keep it upright. When it eventually scraped to a halt Darien's hands were white and his hands were raw from gripping the tether. He looked behind him.

"What...the hell...happened," Idas groaned, currently lying on his back after the crash.

Hekket helped the burly operative upright. "I think we ran something over."

Darien nodded as he unhooked the tether. Using the now red blinking console as a step up, he vaulted over the side and out into the corridor, carbine raised. He looked back down the passage. His torchlight swept over a huge, mangled form in the gloom, limbs bent and cracked into unnatural angles and a viscous yellowy liquid seeping from its carcass.

"That's some serious road-kill," Idas grunted, moving up alongside him. "What is it?"

"It's one of the things that killed all the people who used to live here," Darien replied simply. A rumble passed through the hall, shaking the ground beneath him and he indicated the nearest passage. "We need to keep going and get up into radio range. We've got to warn everyone on this rock that it's time to leave."

"Speaking of," Idas said, turning to face him. "Just what did you find down there? What is the Leviathan?"

Darien shrugged. "I have no idea what it is. All I know is that it's a monster the size of a stadium and we woke it up." He shouldered his carbine and motioned with his head down the connecting passage. "And that means we're leaving, right now."