The primarchs ran at the great monster as it reached for them. It smashed its colossal sword at Guilliman. He rushed under the swing. The sword buried half its length in the flagstones. They melted into gibbering flesh. Warp flames rushed outwards from the gap. Guilliman fired upwards with the Arbitrator into the daemon’s wrist. He struck the limb with the Hand of Dominion at the same time. Muscle and bone parted. Ichor gushed into Guilliman’s face, bubbling his skin with acid. Severed from its master, the sword exploded with a wave of uncontrolled energy.

The daemon screamed and struck at Guilliman with its immense claw.

Guilliman threw himself to the side, but the edge of the limb clipped his shoulder, smashing him down. His fall drove a groove into the floor. He rolled to his left just as the huge arm came at him again, pulverising stone, shaking the walls of the Delphos.

As Guilliman regained his feet, the Lion leapt onto the back of the beast. Shrieking in rage, it whirled its giant mass, trying to shake the primarch off. It horns slanted backwards over its head, and the Lion had seized one of them. His cloak billowed behind him as he clung on with his left hand. His right raised the Wolf Blade. ‘I hunted greater beasts than you on Caliban,’ he shouted, ‘and I slew them all!’ He sawed into the rear of the daemon’s neck. It reared up, scuttling backwards on four of its legs. It slammed into the temple wall, crushing the Lion between its bulk and the masonry. The Wolf Blade kept snarling. Gouts of ichor and shredded flesh splashed up on the stone.

The daemon looked straight up. Serpent and lightning, its tongue whipped out of its mouth. The hall strobed with violet and green light as the tongue lashed behind the daemon’s head. The wall burst into flame. It limned the silhouette of the Lion as he drove the Wolf Blade deeper into the daemon’s neck.

Guilliman pounded over the floor after the great daemon. Whirlwinds of fire and flesh tried to stop him. He held the trigger down on the Arbitrator. The stream of explosive shells shattered their forms, clearing his way.

Above him, two of the creature’s massive, piston-driven legs flailed in the air. They clashed together, and when they did, lightning flared again.

The movement of the legs, the timing of the collisions, the height of the daemon and the arc of a jump were the givens of an equation. Guilliman saw the vectors of force and momentum. At the moment of his leap, the equation was resolved.