"Eldrad Ulthran screamed as the ritual reached its crescendo. All around, the crystal sands of Coheria glowed bright. A bow wave of spiritual power rippled across the moon as every dead craftworlder since the Fall lent a measure of its sentience. But a vital voice in the choir of his psychic melange had been silenced, and the blessings of the Laughing God were fading away.
Wraithbone runes whirled around Eldred burning to smoking ash one by one as the High Farseer struggled to hold the ritual of awakening rogether. His mid was aflame, the skies above bursting in to bright orange fire in sympathy. Psychic energies heated the planetoid to volcanic temperatures. The moon became a psychic sun, a signifier of a new dawn. Somewhere, in the bottomless soulscape of the void, Ynnead stirred to wakefulness.
Another sum blossomed on the cusp of fate, far smaller, and filled with malevolence. Eldrad opened one eye to see a plasma sphere burning towards him. He directed a portion of his psychic focus into his rune armour to dissipate the blast. In that act, he failed. The emerged consciousness of the god splintered, its full apotheosis denied.
The crystal seers shattered with terrific force even as Space Marines sprinted for their assault craft. Eldrad reeled, stumbling blindly through the webway gate behind him as the planet ignited with white fire. The last thing he saw was a vast and solemn constellation losing cohesion, a single bright point from within it shooting away into the far reaches of the cosmos."
So I finally got Death Masque on release. If anyone was as curious about what takes place in the boxed set as I was, this is the conclusion of the story.
TL;DR Eldrad learned of a moon covered in psychoactive sands with similar properties to spirit stones. He tries to use the moon as a vessel for Eldar souls from the infinity matrix, in order to bring about the awakening of Ynnead. The Deathwatch team finds him in the midst of his ritual, the harlequins defending him are killed, the ritual is interrupted and the moon explodes.
Does a kernel of Ynnead emerge from the incomplete ritual?