Darien stood at the edge of the water, breather mask fixed to his face and carbine in hand, grimly turning over in his mind what they were about to do.

"You sure about this?" Idas asked, clearly not thrilled by the prospect of joining him in the water.

"Not exactly."

"The jackhammer's not designed to fire underwater."

"I know that. Use your side-arm."

The other boy looked at him as though he were insane. "A side-arm? Did you see the size of that thing?"

"We're not trying to kill it," Darien countered. "We're trying to distract it." He looked left and right at the other operatives lined up at the water's edge. "Everyone clear on the plan?"

"What, going to play run-rig with a lobster the size of a B-12? Yeah, sounds great," Niamh muttered.

He ignored her and, when no further objections were raised, he waded gently into the water, carbine in one hand and the flat disc of a motion sensor in the other. The biting cold seeped through the protection of the dry suit, but his mind was focused elsewhere as he submerged, his sharp eyes instantly hunting for any kind of threat. Torch lights sliced into the gloom as the rest of Hammerhead squad followed him into the depths. They griped and complained as much as anyone else, but when it came to carrying out his orders, he never had to question their resolve. Even Brannigan hadn't so much as hesitated.

The micro jets eased him forward at a steady pace. On either side of him Idas and Niamh floated in an arrowhead shape. Mirroring the formation several feet below the other three operatives drifted into the beast's lair.

"Hekket, check the first room," he ordered. "We'll cover you."

"Copy that."

From his vantage point Darien watched as they approached the first pitch dark aperture with obvious trepidation. Hekket took the central route, with his companions flanking to either side of the enormous door frame. Their lights carved into the shadows but the monstrous crustacean did not reveal itself. They drifted inside, out of sight and Darien turned his attention to making sure their quarry didn't blind-side them from further down the passage.

Seconds ticked by and he waited there in the icy darkness. Through the Blink goggles his sharp eyes could see under water as easily as if her were on dry land, but the lack of light kept a knot of tension in his stomach. He let the beam of his torch crawl lazily through the gloom but all he found was more gently rippling water.

"The room's clear," Hekket's voice speared over the comm after a couple of minutes. "No sign of life; nothing on the motion sensor. Looks like some kind of...manufacturing area. Some big machines, powered down right now."

"Copy that." Darien rotated left and right, motioning Niamh and Idas forward. He propelled himself forward at the head of the triangle and fifty metres down the passage they came across a second doorway. Further in, things were now completely black and only the operatives' gun mounted lights and mono-rigs illuminated their way.

Part of him wanted to just jet for the far end of the corridor as fast as they could, but the more rational side of his brain told him that was exactly what a big predator would want. If they scattered, if they acted with panic and didn't cover all their bases the thing would try and pick them off. So he led Idas and Niamh into the mouth of the next doorway and shone his light inside.

The circle of sickly white passed over a number of burnished brass-coloured consoles. Some of them looked cracked and damaged; all of them had dead screens. He slid inside, keeping one eye on the motion tracker's display. The flat, dark disc showed the six white blips of the Blink operatives, but nothing else nearby. If the thing was here, it was staying very still.

A pang of regret tugged at him as he began to move through the consoles. Even these comparatively small machines had a kind of sad majesty about them. Large buttons dotted their surfaces, but on one he spotted an impression that could only be some kind of hand print. The shape had the wrong number of fingers – only three – but a definite opposable thumb and humanoid shape. He wondered what secrets they might contain, what magical things they might unlock. As advanced as human-kind was, there was still so much they didn't know; didn't understand. Maybe in this vast alien tomb they could find some answers.

Darien shook those thoughts away, focusing on the task at hand. Niamh and Idas glided off to either side, lights arcing across the consoles as they went. They swept every dark crevice of the room; all the spaces that were large enough to hide such an enormous animal, but the room remained mercifully empty. Darien felt his body relax and he let his eyes wander over the alien consoles once again. If only they could get one of them working...

"Darien," Hekket's urgent hiss sounded in his ear making him jump.

He closed his eyes for a moment then spoke. "Go ahead."

"We've got movement out in the hallway."

"Visual?"

"Nothing, but the sensor shows something's moving around but the reading is partial – intermittent. You'd better get out here."

"Copy." He looked down at his motion tracker again and sure enough, a seventh signal had appeared. Whatever it was, the device was struggling to register it properly. The blip seemed to fluctuate in intensity – one moment a definite signal, the next little more than a weak echo. "I've got the same reading. We're coming out."

When he turned he found that Idas and Niamh were already waiting by the door for him. The micro jets propelled him back into the main passage and he locked onto the three torch beams that seared through the water half a dozen feet above him. Right now the other three operatives were arranged in a defensive triangle, facing outwards. He glanced at the motion tracker again and frowned in confusion. The reading from a moment ago had disappeared.

"It keeps appearing and disappearing," Hekket said. "I don't get it."

"Me neither." Darien shook his head. "Alright, everyone, circle up. I'll take point. Hekket you're at the back. Everyone else, fill the gaps and stay close together. And keep your eyes open for that thing."

He had a very uncomfortable feeling that suddenly the hunters had become the hunted. The operatives drifted through the darkness in an eerie quiet, the only sound the low, barely perceived hum of the micro-jets in their suits. Glancing periodically at the motion tracker he caught glimpses of the strange reading, that he had to assume was the animal, moving closer to them. It would vanish, then reappear a few metres closer, and then vanish again. It didn't make any sense.

"Darien, that thing is closing in on us," Hekket warned.

"Then where the hell is it?" Brannigan cut in and he could here the panic creeping into her voice. "I can't see anything down here!"

"Just stay calm and stay in formation," Darien ordered sharply. "Keep sweeping your points. The thing is the size of a shuttle – it's not likely to sneak up on us." Even as he spoke, however, his mind was racing trying to figure out the strange readings on the disc display. It was close enough that they should have seen it. Hell, they should have felt the tremors in the water from something so large. Instead, they seemed to be alone with nothing but a white blip on a screen to tell them otherwise.

He came to a halt abruptly, and the others followed suit, locking into their formation and scanning the area. The display showed that the creature was barely ten metres ahead. Darien aimed his carbine where it ought to be but just saw more dark, empty water.

"It's right on top of us," Amber cut in.

"Then where is it?" Idas snapped back. "I'm looking straight ahead and there's not a damn thing here."

"We should make a break for the stairs," Brannigan said. "This isn't right-"

"Cut the chatter!" Darien barked, silencing them instantly. He glared into the water, racking his brain for a solution. What could account for it? There had to be something. While he didn't get a good look at the thing that had been chasing Amber, he'd seen enough. It was no ghost.

Then he heard a strange sound, a kind of muffled splash, but he couldn't pinpoint where it had come from. He glanced around and his eyes spotted something metallic glinting in the shadow. A small piece of broken rock, maybe the size of a fist, sank past him, and he stared at it for a moment until the realisation hit him like a punch in the gut.

He looked up.

Directly above them a long gash in the ceiling tiles gaped, and as his light cut into the oily blackness he saw the creature they'd been hunting. His eyes widened in horror. The torch beam caught the monster right in its hideous face, revealing a barrel shaped head surmounted by a gaping maw, inside which a series of enormous, fang-like teeth were arranged. Pincers that would have been better suited to industrial digging equipment hung out in front of it, hanging open in readiness to clamp down and crush anything unfortunate enough to fall into their grasp. Two long, tentacle-like antennae writhed in the water in front of its beady cluster of eyes.

There was a split-second of inaction, then the massive crustacean burst from its refuge in a whirl of foam.

"BREAK!" Darien roared, pivoting back on his heels and firing a shot from his carbine straight into the creature's onrushing maw.

The operatives burst into motion like fish evading a shark, scattering in all directions as the colossus came ploughing through the water between them. He managed to keep track of Idas in the confusion and he jetted over to the other boy, all the while trying to keep an eye on the motion tracker. The reading was definite now – the stone walls in the passage above their heads must have been shielding the monster from their instruments.

He frantically flicked his light back and forth as he caught glimpses of violent movement in the gloom. Then he heard a piercing scream rip over the comm band and he hurled caution to the winds. Grabbing Idas, he pointed himself in the direction of the monster and cranked his jets up to maximum.

They tore through the water, closing in rapidly on the melee and another scream rang out. Darien willed himself desperately onward into the fight, and he soon spotted the flare of lance-carbine discharges within the water.

When he reached the other operatives his heart jolted when he saw that the creature had managed to trap Niamh around the leg in one of its huge claws and she flailed helplessly in its grip as it hauled her back towards its hideously fanged jaw. He could see Amber and Hekket trying to distract its attention, jetting left and right to avoid the second flailing claw. They fired lances where they could, but the projectiles didn't even make a scratch in the beast's armoured hide and it seemed to just be ignoring them like a human ignoring a fly. He couldn't see any sign of Brannigan.

Right now he couldn't dwell on it. They needed to do something and do it now. Niamh screamed again as the grip around her leg pressed tighter, but even now she retained enough of her fiery nature to jam the boot of her free leg against the creature's head, holding herself away from the gnashing jaws. He took one look at the chaos and formed a plan. He was not about to lose his second in command to some mindless brute in the depths of an alien ocean.

"Stall it," Darien said, grabbing Idas by the shoulder. "Keep her away from those jaws! I've got an idea!"

The hulking boy stared for an instant, then nodded, shrugging his jackhammer from his back and launching himself into the fray. Darien set off in an arc in the opposite direction. Side on he could see the monster was easily six metres long, with a body made up of a series of definite sections where its plates of armour met. As it moved he could see the gaps open and close. He readied his carbine and sped around behind it like a guided missile.

As he closed in he saw the thing send Hekket spinning head over heels through the water as it landed a thunderous blow from its free pincer. Despite the terror at what he might see, he looked back towards its baleful head where Niamh was still held captive. The monster reared back, and slammed her against the wall, dislodging the foot that was holding her distant, but even worse, it tore the breather mask from her face.

Desperation wrenched at him as he zeroed in on his target and shot a lance at one of the plating gaps. The thing arched at the wrong moment and the lance impacted harmlessly against its outer armour. He glanced again to the head.

His eyes widened in amazement when he saw Idas suddenly emerge in between Niamh and the huge jaws. He had his jackhammer in his hands. While the weapon couldn't fire underwater, Idas found another use for it. Darien watched as his friend jammed the bulky gun into the thing's jaws, wedging them open for a few more precious seconds.

That gave Darien a tiny window. He couldn't just keep taking shots at it hoping to kill it. He needed to do something decisive, and immediate. Abandoning his carbine, he instead yanked his combat knife free from the holster on his thigh and made a beeline straight for the back of the crustacean's head. His eyes locked onto the two writhing tendrils of its antennae. The back of its enormous body loomed larger with frightening speed, but he didn't slow down.

In one fluid motion, he clamped his free hand around one of the fibrous, flailing appendages and pulled it taut. As he swept over its head he hacked down and severed the left antennae with a single vicious stroke.

Instantly the colossus released its grip on Niamh and reared back, flinging Idas away and letting out a strange rumbling sound that shook the water all around it. The huge jaws clamped down in pain, bending the structure of the jackhammer in half, but Darien's intervention bought them the time they needed.

"Everyone out!" he yelled through the comm. "The far exit, now!" As the creature thrashed in pain he angled himself around its armoured hide and down toward Niamh who was floating, dazed from the impact. Without slowing down he caught her under the arms, pulled her close and rotated to fire them both in the direction of the far exit. He felt her hands clamp down around him and she buried her face against his combat vest as they ripped through the water as fast as the jets would carry them.

He had to trust that the others would follow his command – he still hadn't seen any sign of Brannigan since the chaos began. Trusting that if she wasn't in the grasp of the creature she would be safe, he concentrated on getting his companion out of the water while he still could.

They burst out of the water into a welcome blaze of light from the pyramidal nodes, then crashed to the ground in a heap. Niamh rolled away onto her front, wretched, and coughed up a mouthful of water. Darien hauled himself to his knees and was about to move over to her when he saw a figure standing a few meters further into the passage. He turned the light from his carbine on the shape.

And he saw Brannigan staring back, her carbine clutched in shaking hands as she aimed down into the water.