Curze was shaking his head. He staggered against the altar. He looked as if the light had dealt him a mortal blow. He was ­staring at the portal, his sunken eyes glittering with anger and horror. Guilliman advanced on him. ‘Tell us what will happen,’ he said.

Curze looked up at him with contempt. ‘I don’t know.’

The Lion seized his chain. He bent Curze backwards, arcing his back to the breaking point. ‘You don’t know? You know I won’t kill you,’ the Lion said. ‘And you know I will make you wish I would. Answer my brother!’

‘I don’t know,’ Curze roared. His anger and confusion were real.

‘He’s telling the truth,’ Guilliman said.

The Lion threw Curze back against the altar.

The Night Haunter struggled to stand. He was a ragged shadow in the hard light. ‘If I knew he would fail, I would throw it in your faces. You’re all fools, and he’s the greatest fool of all.’

‘Why?’ Guilliman asked.

Curze whispered, ‘Because he might succeed.’

Corruption draped the halls of the ship. Sanded skins hung between iron spikes that reached from the walls like claws. Sanguinius tasted his blood, and the viscous slick of the air. He smelled scorched ozone, expended fyceline, burning flesh and the stench of rotting souls. The hull of the Vengeful Spirit rang with the clash of blades and the roars of men. A huge icon, the eye of Horus, stared down on Sanguinius as he crossed the threshold into the throne room.

Horus was there, waiting, as he always was, as he always would be until the end finally came.

The brothers fought, and warm blood coursed down inside Sanguinius’ armour. He struggled against the sluggishness of his limbs. His lungs struggled to pull in the foetid air. His hearts beat like pounding stones in his head.

Most acute of all the sensations was the agony of Horus’ blows. Sanguinius knew every step of the fight, every strike and parry and counter-attack. Though his body reacted to the immediacy of the duel, his mind looked at each moment with the despair of total familiarity. Each second was a painting he had studied to the ­minutest detail.

And still the death blow came as a brutal shock.

Sanguinius died, and then he fought again, and died again, and died again. Death was a terrible refrain. He was trapped in a hymn to the triumph of dark gods.

But on Pyrrhan he had found a way out of the trap, a way of disrupting the refrain. He reached for that memory. He seized upon that single, precious future where he killed Horus, and he made it real. For the second time, he experienced the impossible victory, and the surge of hope that came with it renewed his strength. He slew Horus and grew stronger yet. The weight of countless repetitions hurled his death at him once more. In rage and determination, he fought back.