The omnipresent rumble drifted from every orifice and the noise of biological processes was thick in the air.

Uriel could feel a nascent claustrophobia as the walls of the ribbed passage contracted in time with the ramble, expanding again as though they were in some great breathing organ. Steaming jets of liquid sprayed them as they passed from the passageway into a wide, necrotic chamber of crackling gristle and pulped meat.

Row upon row of ruptured egg sacs and niches with cancerous organic pipes hanging inert within them lined the walls of the chamber from floor to ceiling.

'What is this place?' asked Henghast.

'They slept here,' said Damias, sweeping his softly chiming auspex around. 'They slept away the years while they travelled to Tarsis Ultra from wherever they came from.'

Uriel saw Damias was right as he spotted a tyranid warrior organism in one of the niches, its flesh withered and dead. Its four arms hung limply at is side, its bony head slumped over its shoulder.

A sudden hissing motion rippled through the walls, a greenish glow building from the smoke that drifted at ankle height. At the far end of the chamber, a fleshy fold of bone lifted aside and a wash of stinking chemicals spilled into the chamber carrying a tide of screeching tyranid creatures.

'Captain!' yelled Pasanius as he bathed them in flames.

Alvarax and Pelantar braced themselves and sprayed the creatures with shells from their heavy bolters. Uriel fired into the mass of aliens as a host of the ventricle valve doors rippled open and yet more beasts poured into the chamber.

A giant beast bounded towards them, its armoured carapace low and armoured like a scorpion. It bounded towards Jagatun, who ducked and slashed its soft underbelly with his razor-edged tulwar. Looping organs spilled from the wound.

Henghast howled and slashed his power sword through its body, dragging Jagatun to his feet while firing his bolter with his free hand. Pasanius fell back, each step accompanied by a spray of liquid fire into knots of screeching aliens.

Uriel blazed away at the creatures as they poured from the walls to assail them. He didn't know how many beasts the hive ship had at its disposal, but he knew they could not afford to find out.

'Deathwatch, fall back!' he ordered.

Alvarax and Pelantar backed away, firing as they went and closing on Uriel.

'Brother Damias!' yelled Uriel. 'Which way?'

Damias was blood-streaked, his power fist coated in alien gore. He consulted the auspex and said, 'This way.'

He set off through an oval hole in the wall as Uriel called, 'Everyone through here!'

Henghast dived through the hole, followed by Jagatun. The roar of heavy bolters covered them before Pelantar ducked into the gap. Uriel pushed Pasanius through and shouted, 'Alvarax! Come on, we are leaving!'

Alvarax raked his fire over the attacking beasts, his aim sure. Dozens of aliens fell, blown apart by his sanctified shells.

Then the ground opened up beneath him and he was gone, sucked into the depths of the ship.

Uriel shouted, 'Alvarax!' and moved to go to his battle-brother's aid, but a strong hand gripped him and hauled him back.

'He's gone,' yelled Pasanius, 'Come on!'

Uriel nodded and pushed into the close confines of the new passageway, feeling his way by touch rather than sight. He heard an oozing sound behind him as muscular contractions pulled the passage way wider to allow more of their pursuers to chase them. Pasanius pushed him ahead and turned to fill the passageway with flames. Screeching howls followed them as aliens burned. The fleshy passage shuddered in sympathy with their pain and Uriel was suddenly reminded of something Kryptman had told him before they left Tarsis Ultra: 'As you penetrate deeper into the ship, its nervous system will become more sophisticated. It will feel pain the closer you get to its centre.'

He followed his warriors as the passageway sloped downwards, the soggy texture of the ground squelching as he ran. He heard gunfire and saw a glow from up ahead as the passage widened into a vein-ridged chamber with a pulsing, mushroom shaped organism at its centre.

A score of dead creatures littered the ground before the thing. 'What is that?' asked Henghast.

'Does it matter? They were guarding it so it must be important to them,' said Jagatun, slashing his tulwar through its stem. Plumes of spores erupted from the organisms severed stalk and enveloped Jagatun like a cloud of buzzing insects. He batted them away before doubling up as the surface of his armour began corroding before Uriel's eyes.

He heard the White Scar's screams over the vox as the spores devoured him from within, his filters and rebreathers no defence against such a deadly attack. The Deathwatch backed away from the clouds of corrosive spores, unable to help their stricken battle-brother. Pasanius fired his flamer, consuming them in a cleansing burst of promethium.

Chittering screeches from the sucking passageway they had just come from echoed towards them.

'This way,' said Uriel plunging into a ridged opening in the far wall, emerging into a long, curving passage, knee-deep in sloshing fluids. Fronds of cilia dangled from the roof and walls of the passage, waving as though in a gentle breeze. The sludgy liquid flowed away to the right and Uriel waited for Brother Damias to join them.

As the Deathwatch assembled, Damias led them to the left, splashing through the foetid ordure against the flow. Wormlike organisms swam through the sludge, latching onto their armour and attempting to feed.

The Space Marines plucked them from their armour in disgust. They were annoying but hardly dangerous. Uriel pushed onwards through the circular tunnel, the fronds above him brushing against his helmet.

He halted as he heard a strange sound over the constant ramble of the hive ship. It sounded like distant thunder, like standing at the end of the Valley of Laponis on Macragge and listening to the noise of the far-off Hera's Falls.

As he realised what it was he shouted, 'Hold on to something!'

He punched his fist through the tough walls of the veined passage and gripped a handful of the hive ship's substance as hundreds of tonnes of organic waste thundered along the passageway towards them.

Snowdog hustled the wounded men up the stairs to the upper levels of the medicae building, wondering how long they had before the tyranids got here. The damned alarm bells were still ringing and he smashed the butt of his gun against one until it shut up. Jonny was on the landing above him and Lex was busy wiring the main door of the building with the mother of all explosive devices. Tigerlily was keeping an eye on Silver who was now stable, but still unconscious. He had no idea where Trask was, but didn't much care one way or another. He still carried the backpack filled with valuables taken from the crashed starship, so it wasn't as though Trask was off stealing that.

He pushed his way down to the vestibule, seeing the skinny shape of Lex still working at the door.

'Lex, whatever you're doing, do it quicker, man,' he said.

'Hey, I'm going as fast as I can. You know, if you helped, I could get done quicker.'

'No way, man. Me and explosives? Forget about it.'

'Well thanks for offering anyway,' sneered Lex.

'No problem. Everyone off this floor?'

'Yeah, I think so. Everyone except that crazy sister.'

Snowdog pushed his way into the main ward area. The place was deserted except for Sister Joaniel, who stood behind the central nursing station with a plain wooden box before her.

Snowdog jogged towards the nursing station and slung his lasgun. 'Hey, sister, we don't have time to hang around here. Time we was gone.'

'Is everyone safe?' asked Joaniel, tears streaking her face.