Horus studied him, examining the dense lines of text tattooed across the Word Bearer’s face and neck. "I admit I am displeased at this turn of events. Sanguinius’s death would have served many purposes, even if my vanity was one of them." He grinned, at once malicious and self-deprecating. Then his manner turned cold. "But so be it. The Angel will face me in battle before our campaign ends. Only one of us will survive."
"That could have been avoided," Erebus offered, attempting to make back the ground he had given up.
"Do you think I am a puppet?" said Horus. He nodded at the Red Angel. "A weapon to be commanded? I think you may. I think you must be reminded of your place in the scheme of things."
The Warmaster’s hand shot out and snatched at the hilt of a dagger sheathed at the Dark Apostle’s belt. Erebus gave a gasp as Horus took his athame and turned it in his grip, letting the warp-touched blade catch the chamber’s ill light.
"You let the mask slip, Erebus," he told him. "You showed yourself to me. I saw what you show them." Horus touched the tip of the dagger on the Apostle’s cheek and he flinched away as it burned him. The Sons of Horus were suddenly there at his back, blocking his retreat.
For a moment, the Word Bearers legionaries in the chamber hesitated, hands falling to their weapons, ready to defend their master, but Erebus slowly shook his head, warning them off. He had to realise what was to come, and that he had no choice but to accept it.
"Let me see that face again," said Horus, cutting a bloody line across Erebus’s forehead, as his warriors took the Apostle’s arms and held him rigid. "Your true face."
With an artist’s care, the Warmaster sliced through flesh and into meat. Though he gasped and trembled, Erebus did not cry out. Horus took the severed edge between his fingers, and like the turning of a page, he skinned Erebus’s face from his blood-smothered head.
The Word Bearer staggered back, his features a ruin of crimson, stark white eyes glaring out and unable to blink.
"The things that whisper in your ear, that you hold in concord with your pacts and your inscriptions… Remind them that they are not the architects of this war." Horus paused as he considered the bloody rag that was his new trophy.
"I am."
~Fear to Tread, by James Swallow~