Kais wondered how his father felt on his first combat mission. Efficient, doubtlessly. Didn’t bat an eyelid.

Never lost his temper, never grew scared or furious. Ice cold, probably. Served the Greater Good with a clear conscience and a rigid application of the shas’ken’to principles of combat. Flawless.

Comms with the Or’es Tash’var were failing, garbled messages becoming little more than static. The path had grown divergent, hooded corridors branching away into blackness, multi-doored chambers leaving the group disorganised and disagreeable. Finally they’d come to a tight vent access that led downwards and away, wide enough for a single shas’la only. The others favoured continuing along the cloistered hallway, relying on their cohesion with each other to sustain and protect them.

Kais felt no cohesion.

The others grated upon him and, worse, the knowledge of his inability to fit in made his guilt more palpable. Operating as part of a unit was an expectation placed upon every tau. “Never alone,” the Auns said. His isolation was a constant reminder of his flaw, and he hated it.

He was in the vent and crawling before the others could even protest. Not that they would, of course. He imagined them breathing sighs of relief as his retreating back diminished into the gloom of the tunnel.

Half a dec later and comms were a distant memory. The bright icons of the others had dwindled in his HUD as their path carried them further away, and in no time at all he was left alone, once more scampering rodentlike through brittle metal veins, his wounded arm aching from supporting his weight. He cut through the pain mentally and forced himself onwards.

Then things went badly wrong. Lost in the belly of an enormous creature, more vast than one mind could ever appreciate, his only sense of location was provided by the occasional breaks in the vent walls: thick membranes giving way to grille-slits and steel gauze openings. Through such indistinct portals he peered out on a world of dank chambers, strobe-lit techbays, anodyne sleeping cells and sterile, chrome-plated laboratories. Gue’la slouched here and there, filthy ratings and crew that seemed more akin to the rats they co-habited with than the pink-faced troopers Kais had grown used to. He scuttled silently through their midst, suit power on minimum to limit noise and heat emissions.

It wasn’t enough when he came upon the Space Marines.

Briefly, he felt a moment of pleasure at seeing their blocky grey-green shapes through the light-striated grille, patrolling a corridor vertex with measured strides — surely their presence indicated that he was on the right path. No mere troopers, he reasoned, would be assigned to guard something important. He nodded to himself and moved on.

One of the Marines swivelled in its spot, helmeted head tilting inquisitively, staring up into the vent. Kais froze.

The two giants appeared to converse, the first pointing vaguely towards the vent then shrugging, movement exaggerated by its vast shoulder guards. Kais could only guess at their discussion.

He tried to move, painful tor’ils of silence and sweat. His heart sounded like a jackhammer in his chest, thumping in his ears and convincing him that the Marines could hear him.

Satisfied at the silence, they began to move away. Kais allowed himself to breathe out slowly, his mouth dry. Buoyed up by relief, his glacial progress carried him past the grille and slowly, cautiously, he began to relax.

The text wafer in his utility pocket slid gently though a las-singed fabric tear he hadn’t even noticed and tumbled to the floor of the duct. It sounded like a cannon erupting in his ear. It was a gong peal, shivering and groaning noisily. It was a planet splitting across its equator, furious resonances echoing and reverberating throughout eternity.

He grabbed for the wafer, fear pulping his senses, even as the first bolter-shells sliced tubules of light spillage into the duct and detonated angrily near his feet.

He bolted, stealthy progress discarded in favour of blind panic. His limbs raised a cannonade of thumps and clangs as he slithered and dragged himself along the duct, gashes and lumps of debris pulverising the metal walls and turning the conduit behind him into a whirlpool of fractured metal and conflicting detonations. Bolter fire roared behind him, filling the tunnels with ghostly echoes and the sharp scent of smoke.

He scrabbled onwards, turning a corner, lurching upwards into a vertical shaft, taking tunnel branches at random with a stream of mumbled curses and groans. There was no rage here, no surrender to the Mont’au impetuosity — only blind panic and helplessness. Again he knew how the clonebeasts felt during the tau’kon’seh, sprinting impotently for their lives. But this time there was no recourse to turn and fight, no clever scheme to even the odds. In this labyrinth of intestinal tubes he was a parasite, at the mercy of any scalpel-wielding surgeon that could detect his movement and cut him out.

He stared at the tight confines and panic gripped him, an irrational horror at the suffocating closeness of it all. He yearned for the clear skies of T’au.

Is this how it feels to be buried alive, he wondered? Is this how it feels to die, lost and alone and flawed, with nothing to recall your existence beyond a decaying body, not even fit for the purity of a funeral pyre?

For the first time in his life, Kais wished he could remember a few more sio’t meditations on the subject of peace.

Shas’la Du’o’tan was so busy thinking of her recent team mate La’Kais, so busy wondering abstractly how it must feel to have such unvented anger lurking inside one’s soul, so busy recalling his shadow-dwindled form as it wormed its way down into the ductwork nervous system of the gue’la warship, that she wasn’t fully watching where she, and the rest of the team, was going.

She turned a corner.

Something came out of the wall and ate her alive.

The vox clicked.

“...ll brothers hear m... eneral alert, general al...”

Captain Mho glanced at his five battlebrothers and armed his bolt pistol. They followed suit quickly, racking bolters and meltaguns with professional relish.

“...nemy in the air-ve... ng the ducts to infiltr... tay alert.”

Mito shot a look at Sergeant Tangiz, who shrugged. He thumbed his vox-caster.

“Mito here — guarding the generarium access-door. Please repeat, brother.”

“...rother-captain, there are tau i... rone-damned air du...”

“In the air ducts, sir.” Tangiz rumbled, huge frame twisting to stare at the various conduits and pipes lacing the ceiling. On a vessel this vast and ancient it was anyone’s guess what each intestinal tube contained. Mito rapped his knuckles against one experimentally.

“Understood, brother,” he voxed. “Stay in touch.”

Brother Iolux, Mito’s youngest squad member, tapped the barrel of his bolter against a wide sheet-steel recess above his head. “Should we breach one, brother-captain? Just in case?”

“Negative. This close to the generarium, who knows what’s contained in each duct? Are you prepared to strike the wrong one, brother?”

“As the Raven wills it, brother-captain. I am prepared to take the risk.”

Mito nodded to himself approvingly. “Your zeal does you credit, brother,” he said warmly, “as does your altruism. However, in this instance caution is our best recourse. It would not do to be responsible for destroying the very thing we are here to guard, selfless or not.”

“I understand, brother-captain.”

“Good. Audio pickup to full. First hint of movement, don’t spare the ammunition.”

The others acknowledged quickly and fell silent, listening intently, watching scanners for any signs of air movement. Mito flicked infra-red filters across his eye-lenses distractedly, disappointed by the lack of obvious targets. This whole operation had been deeply tedious; the sooner he and his company could return to Cortiz Pol and the Fortress Monastery, the sooner they might find action in campaign or crusade. A Marine’s place was in battle, bolter chattering, enemies screaming, not seconded aboard some navy vessel like a worn-out hunting dog, guarding his master’s least valuable possessions.