Artefacts (The Horus Heresy Short Story)

Before the massacre on Isstvan V, the primarch Vulkan returns to his forge on Nocturne to prepare for war against the traitors. However, in light of recent conflicts with his wayward brother Konrad Curze, he looks upon his personal armoury with a startling new clarity. If the wrath of the supposedly loyal Night Lords can be unleashed upon their own home world in a moment of unchecked rage, is it wise for any Legion to have access to such devastating devices as the Engine of Woes, the Unbound Flame or the Song of Entropy?

Read it because
It's a small, personal tale with massive consequences. Framed as a conversation between Vulkan and one of his sons on the eve of Isstvan V, it encompasses Konrad Curze's madness, the destruction of Nostramo, Horus's betrayal, the creation of the role of Forgefather within the Salamanders and the origins of the mysterious artefacts the Salamanders hunt ten millennia later.