A few metres farther down the tunnel, a lone insurgent dropped down from a ceiling hatch, a grenade clutched in her thin fingers.

Bolters roared, loud and throaty down the corridor, shredding the cultist. The grenade went up in the fusillade, the explosion sweeping out in a firestorm. The Salamanders met it without hesitation, shielding the terrified humans with their armoured bodies.

Hundreds of footsteps clattered down to them from the darkness up ahead.

‘Battle positions!’ shouted Kadai.

A ravening mob of insurgents rounded the corner. Further hatchways in the walls and ceilings suddenly broke open as cultists piled out like fat lice crawling from the cracks.

Kadai levelled his pistol.

‘Salamanders! Unleash death!’

A team of cultists brought up an autocannon. Dak’ir raked them with bolter fire before they could set it.

‘Iagon…’ shouted Tsu’gan over the raucous battle din.

‘Atmosphere normal, sir,’ the other Salamander replied, knowing precisely what was on his sergeant’s mind.

Tsu’gan bared his teeth in a feral smile.

‘Cleanse and burn,’ he growled, and the flamer attached to his combi-bolter roared.

Liquid promethium ignited on contact with the air as a superheated wave of fire spewed hungrily down the corridor.

Shen’kar intensified the conflagration with his own flamer. The cultists were obliterated in the blaze, their bodies becoming slowly collapsing shadows behind the shimmering heat haze.

It lasted merely seconds. Smoke and charred remains were all that was left when the flames finally died down. Dozens of insurgents had been destroyed; some were little more than ash and bone.

‘The fury of fire will win this war for the Salamanders,’ said Fugis, as the Astartes were readying to split their forces once again. Ba’ken supported the Apothecary and was standing with the others that would be returning to Aereon Square.

Kadai was adamant that Fugis and the human survivors be given all the protection he could afford them. If that meant stretching his Salamanders thinly, then so be it. The captain would press on with only Tsu’gan, Dak’ir, Company Champion Vek’shen and Honoured Brother Shen’kar as retinue. The rest were going back.

‘I am certain of it,’ Kadai replied, facing him. ‘But at the cost of thousands. I only hope the price is worth it, old friend.’

‘Is any price ever worth it?’ Fugis asked.

The Apothecary was no longer talking about Cirrion. A bitter remembrance flared in Kadai’s mind and he crushed it.

‘Send word when you’ve reached Aereon Square and the gas has been purged. We’ll be waiting here until then.’

Fugis nodded, though it gave the Apothecary some pain to do so.

‘In the name of Vulkan,’ he said, saluting.

Kadai echoed him, rapping his plastron. The Apothecary gave him a final consolatory look before he had Ba’ken help him away. It gave Kadai little comfort as he thought of the thousands of innocents still in the city and their ignorance of what was soon to befall them, a fate made by his own hand.

‘Emperor, forgive me…’ he whispered softly, watching the Salamanders go.