The soldier dropped to the floor, writhing in agony, screaming blasphemies in ancient tongues.
Corbec had his men point every available gun at him, while the Lord-Captain appeared on the scene, demanding the man not be killed for fear of releasing the demon within. As the screams grew louder, more intense, more high-pitched and demoralising, Corbec had an idea to disable the soldier without killing him (yet) - and commanded his men to shoot the soldier's joints. Knees, elbows, shoulders, each collapsed with a "pop" under the targeted lasfire. At least he wouldn't be going anywhere...
With a huge shudder, and more ancient knowledge screamed from babbling lips, the crewman slammed himself off the hard metal flooring. The horrendous, heretical chants were silenced - and in its place more screaming. Not high-pitched, not blasphemous - just the cries of a horribly wounded man. Again, the Ecclisiarchy appeared, and dragged the soldier from the room. Jayne, head of security, followed, and put the poor man out of his misery - the hard report of the bolt-pistol echoing through the barracks. Finally, the psyker arrived - a young Lesser Astropath by the name of Sands. He elected to trail the beast as it escaped, and led the Lord-Captain, Jayne, and Corbec and his men down to one of the plasma drives, in the bowels of the ship.
As they entered, they saw few signs of problems - until Sands pointed out one of the crewmen, at which point he stopped his duties and stood, stock still, in front of one of the plasma conduits. Sands said he would force the daemon to become corporeal, and that they were to shoot both the crewman and Sands if he was not successful. Corbec gladly held his lasgun to the nape of Sands' neck as he worked, drawing the energies of the Warp into both himself and the now possessed crewman.
After a few seconds, a terrible change was wrought upon the engineer. He began to babble in tongues, and his form started to... destabilise. Odd shapes seemed to flicker through his body, until one fully formed - a feathered tentacle in place of an arm. Sands' face spoke of desperation and being overwhelmed, but still he persisted. More changes came and went, until the crewman resembled nothing more than a tumorous growth, still sporting the smiling face of the crewman. Even that finally gave way, splitting down its length to show a beak and an unnaturally long, rubbery neck, dotted with feathers down its length. As waves of fear, dread knowledge, and... hope overcame the crew, Sands did all he could to signal to the guards - he bashed his head into the floor, screamed, and raised a quivering hand. That was enough for Claudia - she commanded all present (Jayne, the Guardsmen, Corbec, herself, and the other engineers) to open fire upon the thing which now writhed on the floor.
It was over in a few short seconds - what they now faced was nothing more than a few blasted lumps of protoplasmic flesh. As they were unceremoniously dumped into the plasma drive, to be burnt into nothingness, she called for any available Ecclesiarchy members to report to the Enginarium and begin the process of cleansing it as best they could (preferably, without killing any more crew members). The Chief Missionary on board, a small man with a large tattoo of the Aquila across his face, took to the job with great relish.
Scant hours later, the ship had dropped back into Realspace, to enter orbit around the world of Piscinius IV - a world almost entirely covered in water. Large Hives, supported by stilts, sat atop the world-sea, dotted all over the planet almost at random. With Allesaunder's help, they located the one nearest the artifact they sought, and began the intricacies of diplomacy. Scans of the ocean to find the starmap were passed off as "sensor recalibrations", and they claimed they were there for a mix of business opportunities and sightseeing.
The Govenor of the Hive, Quint Mularius, invited them down with open arms when they mentioned the opportunities for trade that the ship presented. After a few good hours of unloading (and a few good rolls), the Lord-Captain had made a fair bit of Throne selling essentials and trading in rare materials. To celebrate their arrival, Quint threw a lavish party for the Spire locals, to allow the Lord-Captain to mingle, and to try and present a few of the Spire Nobles the business opportunities they sorely needed. Amongst the chinless nobles, one figure, resplendent in golden armour bearing huge mechanical wings, caught the Lord-Captain's eye. She was informed that he was something of a local celebrity - Jaka Corvus, the "Yeld" (aerial-support) of one of the most popular Spyre-Hunter teams on the planet. The Spyrers go into the Underhive, kill as many human targets as they are allocated, then attempt to return, without getting caught or killed themselves. It is said Corvus has thousands of kills under his belt. Claudia was terribly unimpressed with both the man and the "sport", decrying both as barbaric and implying Jaka might be "compensating" with all that armour.
After some time, Claudia attempted to get an idea about how she would go about retrieving the item she sought from its underwater grave - and she convinced Quint to grant her permission to go on a dive (under the pretence of "catching fish" for her private quarters).
Many more drinks and a few dances later, she invited Quint to her ship (he'd never left the Hive, let alone the planet) in order to talk more about their trip... and in the morning, a combination of hangover, strange surroundings, and paranoia led him to leave the ship under inauspicious circumstances. While he had intended to go with the Lord-Captain, he figured it "more trouble than it's worth". So, Claudia, Corbec, Jayne, Allesaunder, and a few more guards were taken into the briny depths by Yakob, their pilot.
Their submersible might be somewhat armed, but apparently, it wasn't much of a match for the local wildlife - some giant aquatic predator was pursuing the sub, with the possible intent of lunch. Shooting it with the ship's in-built las-mechadendrites prove futile. At the Lord-Captain's request, Yakob pulled the ship into a very quick dive - while Jayne, Claudia, and the pilot were unaffected, Allesaunder simply smiled as he felt the pressure build at his temples, the guardsmen variously yelled and threw up, and Corbec passed out (despite his insistence he simply fell asleep). As they pulled closer to their destination, they caught sight of a large coral reef, covered in weird shapes - closer inspection proved them to be somewhat biological, resembling limbs, torsos, and other body parts. Claudia fancied she could see them moving, though the thought disturbed her more than she let on.
Pulling in closer, they realised they needed to ditch the ship to get inside - so Claudia, Allesaunder, Corbec and Jayne got themselves suited into their aquatic "powered armour" (one-man submersibles, really) and set off. Each suit had a weapon slot - Corbec and Allesaunder took standard lasguns, The Lord-Captain took a flamer (promethium is hot enough to burn underwater, after all...) and Jayne took a backpack-mounted lascannon.
As they entered the structure, the shapes in the coral started to become clearer - faces, the odd fully formed body, some in agony, some perfectly serene. Further inside, they found a large, cleared space, an almost perfect sphere of missing coral. The shapes here started to take a more... alien bent, forming limbs of bizarre proportions and a few faces of strange beauty. As Allesaunder felt a sudden surge of psychic activity, he pushed ahead of the group - only to be knocked from sight by a huge tentacle.
Lurking inside was a beast the size of a shuttle, resembling a seastar with far too many extra tentacles. The deep-sea beastie, threatening as it was, proved no match for the combined fire of the group (even though a solid hit from Jayne split the beast into two independant creatures). After the brief tussle, Allesaunder reached the bottom of the cave, and began digging through the coral. With each fistful he pulled free, the group felt waves of nausea and sorrow, culminating in a deep, harrowing feeling within their souls. As Allesaunder had thought, the coral was some kind of psychoactive creature - further digging would probably send them catatonic.
Claudia had a problem - by the looks of it, the chunk of starmap they had found was pretty big. There were few ways to remove it without causing significant fuss. The crew all thought of the teleportarium... except they didn't have a beacon to use it. With a little bit of quick thinking, however, Corbec sorted that problem - he suggested it be torpedoed down to them, fired inside a macrocannon shell. As you might imagine, a starship opening fire upon a planet caused a certain amount of problems - and even the Lord-Captain's insistence that it was an "unplanned weapons test" wouldn't deter Quint (already highly suspicious). He dispatched the best ordinance he could to combat the starship - a few modified aerial fighters, barely space capable. While they plinked ineffectually at the metres-thick void-shielding around the ship, the Lord-Captain had a thought. They would need the submersible to retrieve the beacon, and the pilot would most likely balk at the thought of assisting the crew that just opened fire on their planet. So, she decided to appeal to his baser instincts - greed.
"Yakob, what are you paid at the moment? You fancy doubling it?"
A quick haggle later, and the Lord-Captain had a new personal pilot, and a stolen submersible for her troubles. As the beacon was put in place, the submersible's vox and pict systems went into an override - and the face of Govenor Quint appeared, enraged and screaming. The Lord-Captain's attempts to calm him down simply made him more annoyed, until she tired of his tone and had Jayne fix the override the Catachan way - a lasbolt.
The ship was eventually teleported back on board. As they readjusted to the pressure (the sub had a built-in pressure room), they could hear a great, thunderous sound outside, like a great storm. When they finally exited the ship, they realised why - to get them and the stone (along with a fair chunk of coral), the Enginseers had to take a solid sphere of matter - including about a ton of water. Luckily, the ship was designed with such things in mind - vents and channels redirected most of it, and no major damage was done to the ancient archaeotech of the Teleportarium - but they did leave many a Tech-Priest in soaked robes, screaming invectives and prayers to the Omnissiah, apoplectic with rage. The ship sat upon the chunk of coral containing the stone - and the Lord-Captain, knowing that such coral could be very valuable, ordered one of the cargo bays void-sealed and converted into a pool of sorts, using their recently-acquired water.
As they prepared to leave orbit, however, a huge crackle of lightning spread itself across the void, and a familiar voice poured from the lips of the Astropath. Deep, booming, and altogether full of itself...
"Lord Captain Black... it's been a long time. You owe me a hand, dear..."
Captain Krawkin's flagship, His Unconquerable Will, was pulling out of the Warp not but a few hundred kilometres in front of them.