It was a small world, spinning about its sun. Just a world like uncounted millions of others; land-masses, oceans, plants and animals. A population of little technology but considerable social advance walked the green and blue planet's woods and plains, occasionally warring amongst themselves, sometimes trading. What made this world unique in his experience was its mixture of sentient species; humans and abhumans, eldar and a typically variation of ork, giant sentient lizards, even sentient birdlife. The Angel watched the pict images scroll even as he gazed down at the little world from his personal observation platform. His father had ordered the IX Legion to observe until his arrival, but not under any circumstances to allow the planet's inhabitants knowledge of the warfleet in system – a unique order in his experience. Father had been unusually tense, almost eager, on receipt of the message of discovery, although for what reason even he could not work out.

The comm-unit chimed. "Lord, we have detected an imminent warp arrival. Signals indicate it is the Iron Blood, and that your father the Emperor is aboard."

Sanguinius smiled to himself. "Thankyou, admiral DuCade. I shall be down momentarily." Perturabo was with his father, then. Good. It had been too long since he had met his taciturn brother. He turned from the observation windows and strolled easily towards his personal lift access.

The long dark warship was devoid of external decoration. Not for its master the fripperies of gold-inset amour-plate, or glittering pearl-white enamels to announce his presence. No. The ten-kilometre length of this warrior's personal battleship was broken only on the face of the command tower, which showed a stylised astartes helmet, shining silver beneath the two-headed eagle of his father's Imperium. All other crenellations and decoration had been removed decades ago, replaced with carefully designed emplacements which maximised fields of fire while providing the finest defensive use of adamantium plate. While his brother's Red Tear was beautiful and decorative, suitable for diplomacy and cajolement, Iron Blood was clearly constructed for only one purpose. War.

And yet. Was there not beauty in functionality? The Iron Warriors, Fourth Legion Astartes, did not fuss, did not make fanciful their armour and weapons. This, their fleet flagship, was very much in the same mode, sleek and perfectly ordered. If an enemy called down Perturabo's wrath, better that they see what they had done before the end. False hope of mercy was dishonourable.

Still, the massively armoured warrior, dark and coldly handsome could appreciate the cleverly designed fleet flagship of his brother's legion as he looked upon it from above. Red Tear from this angle was a winged ruby tear-drop, matching the sigil of the Blood Angels. A master craftsman himself, Perturabo smiled slightly at the effort his sometimes overly humble brother had put into the design and construction of his unique personal vessel.

Behind him the door chimed and opened. He did not have to look round to sense his father's entrance, but did so anyway. The Emperor of Mankind had a smile on his face, and the Iron Warrior primarch raised an eyebrow – for him, the equivalent of an outburst.

"Still curious, I see." The Emperor's voice was pleasantly deep and perfectly modulated, as always.

"Of course. It is not every day that we drop everything and traverse half the galaxy to answer a routine signal. Even a routine signal from one of my brothers."

"No, it is not. And I do not need to be a psyker to realise how much it intrigues you, Perturabo." His voice turned serious, calm but implacable. "But I would not have asked any of your brothers to do this. If this plays out as I hope, or if it does not, Sanguinius and you alone are to know. Whatever happens in this system, never happened, and will never be spoken of."

Perturabo bowed his head wordlessly. The Emperor smiled.

"Come then. I have asked Sanguinius to transport across. Let us join your brother and be about it."

The room was sealed, against both technological and psychic listeners. The two Primarchs stood quietly watching the playback of imagery.

Finally, Sanguinius spoke. "Father, this is all very well, and I grant it is unheard of for a world to be shared peacefully between eldar and mankind, let alone with other sentient species. But I fail to see the point. Should we not land and announce ourselves? This is a primitive world. Why does it merit your close attention? And two Primarchs?"

The Emperor looked at his other son. "What do you think, Perturabo?"

The dark eyes were impassive but held calculation. "I think, my Emperor, that you have been searching for this place, this world, for a long time. Though I do not know why."

A nod. "Perceptive as always. I have indeed. As to why, well, therein hangs a tale. I have never spoken of my origins except in general terms. I was, of course, born on Terra, many thousands of years ago as you know. And always I have known the immaterium. Both of you are touched by that; Sanguinius by the visions that accompany prophecy, and you, Perturabo, alone of my sons, perceive the Eye of Terror for what it truly is."

"Magnus?" started the Angel.

"Sees the immaterium as a resource. He is wrong, and despite his personal abilities, I believe he is blind to its true dangers. You two are not. I still hope to avoid those dangers. But I am not omnipotent. If I fail, then this world is the hope of the galaxy, perhaps of the universe. This 'middle-earth', as its inhabitants call it, must not fall, else all races, all life, will crumble to dust, wiped from the stars in a tide of blood and anguish. Of all my sons, I charge you two alone. Keep this world safe. Let none approach, be they human or eldar or god. No matter what happens."

"God?"

A cynical smile. "There are entities in the immaterium, born of the emotions of countless billions of sentient lives, that consider themselves as such. They are too all intents and purposes, immortal, and capable of actions that one might consider god-like. And they hunger for worship. If I fail, they will ensnare entire worlds, my charge, humanity, perhaps even some of my sons. But I trust you. Alone of my sons, should you two be caught in the trap, you have the will and strength of purpose to hold back yourselves sufficiently to keep this vow I ask of thee."

"You ask us to keep this world untouched and unsullied?"

"For the sake of the galaxy, of all the sentient races, yes. Yes I do."

"You have it," said the brothers in unison.

Sanguinius shivered. One day, he knew, he would walk upon that innocent world, silent and invisible. His father's gaze locked with his own, and he knew, too, that he would fall defending the Imperium, and that his beloved brother beside him would be on the other side. The Emperor's smile was faint but true. Forgive him, for I have treated him beyond even his endurance.

Perturabo looked at the silent conversation, suddenly confused. The swirling Eye that haunted him would claim its due, he knew it now. He would fall to the warp powers. But why were his father and brother smiling at him? Uncertainly, he smiled back, and let his family's arms enfold him.

"Set course for Baal. Remove all records of this world from the archives. We were never here."

The great battle fleet slipped into warp. Behind them, Arda spun on, unknowingly, eternally, protected.