The Characters
Ash Underblade, assassin plucked from a Schola Progenium and trained for murder
Absalom Athanasius, sanctioned Imperial psyker with a talent for telekinesis
Erastus van Saar, ancient and venerable savant who hails from a Hive World of scum and villainy
Sister Lucrezia, a Sister Hospitaller adept at both healing and confronting heretics with a hand flamer
Events
The acolytes continued to explore the Haematite Cathedral after Ash pryied open the rusted door to the sanatorium. Unfortunately, as soon as they entered the northern wing of the cathedral they were set upon by rotting mutants. One of the mutants, Vorkas Hekate, made a direct line for Erastus because the savant was still carrying the hunting rifle that used to belong to him. Ash put a few mutants down with headshots from his rifle; Sister Lucrezia lit some up with her hand flamer. Ultimately, Vorkas proved difficult for them to put down. Erastus gave up the rifle, which Vorkas repeatedly tried to brain him with until he was finally slain.
Inside the sanatorium cells they found a mysterious message scrawled on one of the walls, as well as an image of a bird-like Daemon gouged into the plaster. The final room of this wing was a chamber in which a skeleton was strapped to a medical table. A broken-down auto-surgeon loomed above. Sister Lucrezia determined that the auto-surgeon had been used to perform operations of little medical merit; mostly it had been used to perform trepanations meant to increase the patient's "cosmic awareness."
The group then decided to explore the planetarium tower. Inside was a large model of all the planets in the system; each planet was represented by a human skull encased in glass. Above them, it was apparent that the top of the tower could be opened up to allow the planetarium's telescope to gaze upon the night sky. When the inquisitorial agents started to experiment with moving the planets in the orrery, suddenly Koronath Hekate appeared at the room's desk. Koronath's skin was covered in strange mathematical equations, and his appearance in the room was accompanied by the tower opening and the telescope extending. Weirdly, an unnatural light began to pour into the room from above.
Erastus engaged Koronath in a spirited debate over the hidden truths of the cosmos. Koronath's position was that the stars still had much guidance to provide to mankind, while Erastus insisted that the only beacon of light worth following was that of the God-Emperor himself. Ultimately, Sister Lucrezia ended the debate by turning her hand flamer on Koronath, melting his flesh from his bones. As he sizzled and liquified, he thanked them for giving him much to think about. After he dissolved, he left behind the third portion of the skull-and-cog emblem that would fit into the depression by the canon in the nave.
Their next stop was the library. A little searching revealed a hidden alcove of secret books. Sister Lucrezia attempted to read one, but all she got for her efforts was visions of a galaxy on fire; the book then dissolved into green slime that ran through her fingers. Erastus fared better with the two books he examined. The first book made an unreasonable anger boil up within him; however, he mastered himself when he realized that he had drawn his snub revolver and was deciding which of his companion's he should execute with it. The third book, bound in bronze plates, contained the Tzeenchian theories of Koronath Hekate.
The group returned to the nave, noting that there were now three desiccated corpses sitting on the pews, and fit the skull-and-cog emblem into the matching depression in the wall. A section of the floor opened up, revealing a shaft that went down into the darkness. The shaft looked like the inverted image of a spinal cord, complete with handholds and footholds. A quick test, dropping an object into the shaft to listen for how long it would fall before striking something, revealed that the shaft was quite long.
At the bottom, they found themselves in a small circular chamber lit by servo-skulls. The sound of machinery was very loud down there. A strange map on the wall revealed the Haematite Cathedral's biggest mystery: it was no place of worship, but rather an Imperator Titan! The upper works that they had explored was simply the structures built atop the titan's exterior; now they were in the belly of the Pax Macharia!
As they explored the interior of the titan room-by-room, they found the corpse of Barabus Zanatov, aka "Tauran Hekate." Zanatov's head was missing, but a bolt pistol was by his side and a vox recorder sat in his lap. By replaying the vox recording, they learned that Zanatov had come to the planet bearing a secret uncovered by Inquisitor DeVayne. Zanatov traded his rogue trader riches to establish himself and his crew as the noble Hekate family, all the while building the Black Sepulchre to decipher that secret. He also claimed that the Gilded Cathedral had been built to block the Black Sepulchre from fulfilling its purpose; the Black Sepulchre needed unfettered access to the dark of the Barsapine's night sky. Zanatov also mentioned that he had been pursued by agents of the ruinous powers and the Dei-Phage moved to stop him. Rather than be driven insane, Zanatov resolved to take his own life. The last thing captured on the recording was the chilling sound of Zanatov blowing off his own head with a bolt pistol.
The group also located the genatorium, but the chamber was clearly befouled by Chaos: daemonic ichor ran down the walls and the floor was covered in pulsating flesh! However, in another chamber they were able to restore a cogitator to power; the cogitator explained how to raise the genatorium's shield and replenish the titan's fuel. Donning protective gear, Ash successfully revived the Pax Macharia from its long slumber. In awakening, the titan began to free itself from the "cliffside" that had accumulated around it over the long generations. A mechanical voice called out, telling them to man the "battle stations," as a Daemonic presence was now incoming.
The agents rushed back to the nave, where they saw a one-armed Daemon of Tzeentch rise from the sea and begin to fly on tattered wings directly toward the Pax Macharia. Erastus and Ash sprang into action; Erastus quickly figured out how to make the nave's canon operational, and Ash was ready to fire it as soon as it powered up. When the time was right, Ash pulled the canon's triggers--and the canon promptly exploded, sending both Ash and Erastus hurtling across the room as the canon destroyed itself. Though the canon was now inoperable, it had indeed hit the Dei-Phage.
The Daemon barreled into the nave ON FIRE and badly wounded. Nevertheless, it was still a great and terrible threat to the inquisitorial agents. Though they had managed to grievously wound it with the titan's canon, they were now having trouble piercing through its unnatural, warp-tainted toughness. (Absalom telekinetically hurling a flaming piece of wreckage at it was fairly effective, though.) The Dei-Phage, however, was not having trouble wounding them. A blow from its claw ripped through Sister Lucrezia, and another blow nearly killed Absalom. The Daemon flew at Absalom again to finish him off, but the psyker managed to send all of his kineblades against the horror, shredding it into a mass of rapidly putrefying meat just as its remaining claw grazed him.
Once the Dei-Phage was destroyed, the Pax Macharia began to march through the sea in the direction of the Gilded Cathedral. When the Pax Macharia arrived, it sent the city into a panic. Masses of people were screaming and running, alarm sirens were sounding. The Pax Macharia announced that it had brought the agents to witness what was to follow. The Pax Macharia then charged its Plasma Annihilator and fired it upon the Gilded Cathedral. The Gilded Cathedral was reduced to golden slag. The destruction of the Gilded Cathedral, and the deaths of all who were within it, immediately robbed the city of all light; all that remained was the Black Sepulchre. But what secret did it hold?