Darien couldn't blot out the surge of apprehension he always felt when other operatives Blinked out of existence. Even with all his knowledge and experience there was still a tiny part of him that found the whole business just a little bit strange. Amber and the precision Blinkers from Tundra and Vandal stepped out into the middle of the room, giving each other a wide berth out of habit more than necessity.

He remembered watching Amber do this all those months ago under far more dangerous circumstances, flinging herself into the unknown, billions of miles into the ether because she'd chosen to. She was one of the bravest people he'd ever met, and in an organisation like Blink she had some stiff competition. She caught his eye and flashed a reassuring smile before turning and readying herself for the Blink. By Amber's standards this was a cake walk – a few thousand meters, clearly defined with every distance mapped and locked. He could probably have done it himself, but he trusted Amber explicitly. She had a gift. She could Blink more effectively than anyone he'd ever known.

The boy from Tundra disappeared first, his body vanishing from sight and leaving behind a strangely distorted area of empty space, still catching up with the fact that he was no longer there. Amber went second, then the Vandal operative. Silence hung in the air and he could see the dumbstruck faces of several of the bridge crew. Most of them had probably never seen someone Blink travel before. Tyndall was hiding his surprise, but the way he stared hard at the empty spaces where the three teenagers had just been told Darien that he was impressed. Link, by contrast, made no secret of her amazement. Her eyes went wide and her mouth opened.

"That is one hell of a magic trick," she murmured.

Darien didn't answer. He waited, foot tapping involuntarily against the deck plating as seconds trundled by; waited for the tingle that would tell him Amber was safe. He caught Niamh's eye but his second-in-command stayed impassive, quietly confident. He wished he could lock up his emotions quite so easily.

Then he felt it, the small warm twinge in base of this neck and the sense of connection. He could suddenly feel every inch of space between himself and the Nav-Rod – orient himself to arrive anywhere around it. The distances, the spaces, they were handed to him by the technological miracle. Relief trickled through him and he nodded to himself. It was time to go to work. He looked at the other Hammerhead operatives first.

"Everybody locked on the signal?" he asked.

An enthusiastic buzz of agreement told him that everyone under his command was ready to go. He cast his eyes over Vass and Mina.

"We're all set," Mina told him.

Vass grinned maniacally. "Rock'n'roll."

"Listen up," Darien declared, raising his voice. "All teams check in once all operatives have safely arrived at their locations. From there we proceed on mission. Radio check-ins every thirty minutes unless I tell you otherwise. Be safe, everyone."

The rest of the Blink operatives spread out around the room in a large circle. Darien hugged his carbine crossways over his chest and swallowed a deep breath. Then he let his mind descend into the trace-like state that Blink travel required, and made it happen with a single thought. He felt a brief moment of absence – of not quite existing at all – before his body returned to the physical world.

His feet struck the ground, generating the faint clack of hard soles on stone instead of the metallic thunk of the submarine's deck plating. In a single, smooth motion he opened his eyes and his body uncoiled like a spring. He locked his carbine against his shoulder, flicked the switch of the mounted torch, and scanned the area immediately around him.

Darien looked for only one thing at first. His body didn't relax until he saw Amber, standing with her carbine held loosely in both hands, her body outlined by the glowing blue spear of the Nav-Rod behind her. That was one thing off his check list. Next he let his eyes rove left and right, waiting for the tell tale breaks in space-time where the rest of his team would emerge from.

They came through barely seconds after him in a surge, emerging into the dim twilight of wherever with weapons raised, torches slicing into the gloom as they followed their standard procedures. He was gratified to see that Brannigan arrived without incident, fanning out in textbook fashion, features hard and emotionless.

Only once the other members of Hammerhead were safely accounted for did Darien allow himself to examine the chamber he now found himself in. When he did, he found himself feeling very, very insignificant.

Professor Churchwood's assessment looked to have been correct. The chamber the operatives had Blinked into was enormous, with vast arching beams holding a ceiling that stretched up into the darkness. The circular chamber was as large as the main hangar of Blink HQ, and dozens of doors opened off from it at regular intervals all the way round. He shone his torch over the middle of the floor, revealing a strange mural of interlocking lines and shapes cut into the stonework.

"Now that is impressive," Niamh breathed, gazing around the cavern, her vision aided by the augmented cybernetics that replaced one of her eyes.

"Mappers," Darien said quietly. "Let's not keep the professor waiting for his goldmine." He tapped his earpiece. "This is Hammerhead to Tundra and Vandal. We have arrived safely. Status?"

"Vandal here," Mina replied immediately. "All operatives have arrived without incident. We're starting our initial sweep. It looks like we're in some kind of...honeycomb of passages and rooms. It's not a million miles from an early colonial cluster-block."

"Tundra, reading you loud and clear," Vass confirmed a moment later. "You can tell the prof that he was right. It looks like we've Blinked into some kind of docking area. Doesn't look like there are any ships housed here though. We'll start our sweep now."

"Copy that." Darien was gratified, if a little surprised, to find that the radio transmissions within the complex were coming through cleanly. Hopefully their signal would penetrate back to the submarine and their companions aboard. He clicked through to the next frequency, made a small prayer to whoever might be watching from the stars, and made the call.

"Hammerhead Squad calling the Manitta-Vanna," he said firmly. "Come in please."

It took a few juddering seconds, but to his immense relief a reply crackled through, nowhere near as clear or crisp as the short range bursts within the station, but readable nonetheless.

"Hammerhead Squad, we read you," Link's exuberant voice burst over the comm line. "Status report?"

Darien grinned. "All teams have successfully made it inside the station. We are beginning our initial sweeps of our points of ingress. From what we can tell Professor Churchwood and his team are batting a thousand. They've predicted our arrival zones to a tee."

"I'm sure he'll be happy to hear that."

"Are you receiving a live feed from the mono-rigs?" he asked.

"Indeed we are," Link answered. "At the moment the images are stable, but we're expecting both visual and radio transmissions to degrade the deeper into the city structure you go." There was a pause. "Looks like you've found one hell of an ant hive down there."

"You could say that." He smiled ruefully. "We're going to continue our sweep. All teams are mapping the floor plan. We'll check in every half an hour."

"Copy that, Hammerhead, good hunting. Manitta-Vanna out."

Darien flicked his comm channel back to the local beam and reached into his combat vest, pulling out one of the Blink issue mappers. The device was shaped like a pistol without the barrel, just a handle with a screen four inches across attached to its apex. With each pull of the trigger the mapper unleashed a pulse of high density particles that recorded every solid object in their path, not unlike the old sonar systems on Earth. When the pulse returned the mapper converted the data into length, breadth and depth, creating a three dimensional model of the room and whatever went beyond it.

"Darien." Idas beckoned him over. "It looks like that knock-kneed egghead wasn't joking. The mapper can't penetrate the walls. We can map out this level – the length of the corridors – but the particles can't pass any further. This might take a while."

"We're here for the long haul," Darien answered. He squeezed the trigger of his mapper to test Idas's report, and sure enough, he was rewarded by an accurate depiction of the chamber they stood in and the corridors immediately beyond, but nothing else. "Impressive. No human made this vault, that's for sure."

"Darien," Niamh called. "I think we should start here." She waved the squad over from her position near one of the doors. When they joined her she pointed down the dark passage. "I'm reading stairs heading upward at the end of this corridor. Churchwood has been right so far – the command and control centre is probably housed in the central tower near the top."

"Good enough for me." He stuffed the mapper back into his vest and hefted his carbine, motioning the others forward with his head. "Okay boys and girls, looks like we're not getting out of this. Keep your carbines ready but no itchy trigger fingers, and nobody shoots anything unless I order it. We're not looking for a fight down here. Niamh, you and me up front. Hekket and Idas, stay central and keep mapping as we go. Amber, you and Brannigan take the rearguard."

Like a well oiled machine the operatives dispersed into their positions. Darien raised his carbine to his shoulder and led the way into the mouth of the dark corridor, making a mental note of approval at their new team mate's conduct thus far. As he stepped over the threshold, however, something unexpected happened.

The lights came on.

They stopped barely a few steps into the hall. Looking up, Darien spotted the source. High on the arched bronze ceiling a series of pyramid-shaped nodes rotated gently in their housings, generating a soft cream light that spilled down the gentle arches of the supporting struts. The illumination revealed that the towering walls were studded by the diamond windows they'd observed from the outside. Up close they were truly enormous, and beyond them the crushing weight of Marianas's oceans rippled and swelled.

"You think the lights are automated?" Brannigan murmured from the back of the group.

"Your guess is as good ours, kid," Niamh answered.

Darien tore his gaze from the lights and looked down the corridor. It stretched away for what seemed like forever.

"Six hundred metres," Hekket interjected as though reading his mind. "Then a right and we'll hit the stairway."

"We'd better get walking then." And he set off, leading them into the unknown once again. Their footsteps eddied and echoed up into the arches and the lights continued their languid rotation, creating a strange moving glint that made Darien's eyes hurt. He took care to look up and around the walls, examining more of the strange geometric murals. They were in no language he recognised – not that he'd expected to – and had no pictures or sculptures to give reference. Nonetheless, he made sure he gave Churchwood and the others back on the sub a good view in case it meant more to them.

It took several minutes for them to traverse the length of the passage and when they stepped into the connecting junction more lights came alive in the darkness. The corridor they now stood in branched off left and right, but the main strand continued on for as far as Darien could see before disappearing into darkness. The whole place seemed to have been designed to impose and intimidate; to impress upon all comers the power and majesty of those who'd built this strange, under-sea world.

As instructed, they took the right hand passage and found the base of the stairwell, exactly where it should be. At a glance, Darien could see the steps were not built for human beings – they were too large. He could still clamber up them, albeit somewhat awkwardly, but they had not been built to accommodate human legs. The stairwell was shaped like a square, with the steps climbing the walls in a right-angled spiral. Pausing at one of the windows, Darien peered out into the depths.

Though the light in the passage was steady, it was quickly swallowed up by the ocean outside the walls. He could just make out the other hive-like clusters of the city's structure in the gloom.

Then something huge swept past the window in a torrent of water.

Darien leapt back and instinctively levelled his carbine and he was not alone.

"What the hell was that?!" Niamh hissed.

Darien double-tapped his earpiece. "Hammerhead to Manitta-Vanna. Come in, Link."

"Reading you loud and clear."

"Did you see what I just saw?" he demanded.

"Hang on...eh, yeah, got it. Looks like one of the local whales put on a show for you."

"There are whales down here?"

"Well, yes, this is an ocean planet."

He bristled at the woman's nonchalant reply. "And no-one thought it might be worth mentioning?"

Lieutenant Tyndall's coarse voice grated over the comm in reply. "You're inside the city, operative. The whales are in the ocean. You don't need to concern yourself with them. Besides, we've studied them extensively – they're peaceful, no threat to the research base and certainly no threat to you while you're inside that place."

"Copy that. Hammerhead out," Darien growled. He looked at Niamh and shook his head in annoyance before pointing up the stairs with his carbine. "Let's keep moving. We were bound to get a few surprises down here."

They climbed the oversized steps for several more minutes, ascending three floors until Hekket halted them and pointed to an entrance currently shrouded in darkness.

"In there, Darien," he said. "I'm reading more stairwells, a denser arrangement of corridors and dozens of rooms."

Without a word, Darien rotated and stepped into the next corridor with Niamh close on his right shoulder. Again the lights came on as soon as his feet struck the floor on the other side of the doorway and he was beginning to think they must be automated. Other than the pyramidal nodes – and the whale – there had been no sign of life.

The light revealed a broad passage with dozens of smaller doors lining the walls on either side in a staggered arrangement. Although smaller than previous entrances, each one still loomed around twelve feet in height, and he saw diamond-shaped panels built into the wall on the left of each one. The panels bore what looked like buttons, packed with triangles that each had a different geometric glyph carved into their structure.

"They look like control panels," Niamh said.

Darien nodded. He shone his light into the room, revealing what looked like some kind of office area. Three rows of standing consoles shaped like hexagonal prisms filled most of the space, and he could see panels of grey built into the brazen walls.

"Fan out," he said. "Hekket, Amber and Brannigan, take the rooms on the right. Niamh; Idas, you come with me. Make sure you shine your lights over every nook and cranny – give the good professor plenty to work with. But-," he turned to them all, "don't touch anything."

They split into threes and worked their way down the passage for what felt like an age, peering into rooms identical to the first. Lights greeted them, but the consoles themselves yielded no secrets. Right now he had no intention of toying with the alien systems, not until the scientists back on the Manitta-Vanna had looked over the feeds. The one thing he noted, however, was that there was no sign of the city's inhabitants, whoever they were. The place was uninhabited by either the living or the dead.

The squad recombined at the far end of the passage where a gentle ramp sloped up towards a much larger set of doors, this one standing easily twenty feet and spanning the mouth of the passage. Falling back into their original order they moved up into the next section of the silent, tomb-like halls. The huge arches reminded Darien of the old cathedrals and temples of Earth – grandiose, but melancholic – monuments to a long forgotten past.

"Three hundred metres ahead," Idas declared. "Then we'll hit a closed door. I'd say that's worth looking into."

"On me." Darien motioned with his carbine and led them onwards.

This new hallway had one thing wrong with it, however. Halfway down the cavernous space he could see a section of the lights seemed to have failed, leaving a segment perhaps fifty meters long shrouded in darkness. The floor looked even darker than its surroundings. As they approached a pang of realisation twanged through Darien's body. A heavy sigh escaped his lips and he let his carbine drop as he reached the edge of the blackness.

"Well, that's just...terrific," he muttered.

Ahead of them an entire section of the stone floor had collapsed, leaving a yawning black pit between them and their destination.