The story behind this is in one of our earlier campaigns, we were tasked by our Inquisitor with uncovering the location of a supposed Cult of Slaanesh on a hive world whose members contained a large number of nobles and dealing with it appropriately. Turns out the cult wasn't so much a cult so much as a really raunchy club that was unknowingly the base for a REAL Slaneeshi cult.

One of these nobles was Lyra Mae, a rather "proper" woman who had her hands in the arms dealing business. My character(a Sister of Battle) and this NPC became somewhat close. I wrote this before the campaign was even finished, just as a fun bad end scenario for Lyra. Some people tell me the last paragraph is optional, so go ahead and don't read it if you like how it ends before that.

The doors are thrown open forcibly, the servant standing at attention knocked to the ground, falling back with the faint squeak of bare flesh on marble. The woman strode past with purpose, form held high as four men followed her. She wore simple, yet high quality robes of pure white, trimmed by a red the color of blood with hair that matched her clothing flowing to her back. An azure fleur de lys tattoo upon her cheek, just below one of her bright yellow, slitted eyes, marked her as one of the Adepta Sororitas and the large caliber autogun strapped to her back reinforced this. Her face, unscarred and beautiful, held an expression of barely contained rage as her large strides carried her through the mansion with heavy footfalls and she sends one of the party, a man almost entirely composed of mechanical and bionic parts hidden away beneath a hooded red robe, away up some stairs.

Another door is thrown open, this time off its hinges and it crashes to the ground, the room's only occupant startled out of her seat as she drops the book she was reading. She surveys the entering party and blinks, a confused expression crossing her face almost immediately after the noise settles.
"Sister, I did not expect you back so soo-"
"You dare speak to me after you betray my trust?" The white haired woman speaks in a raised voice, hostility dripping from every word. "Restrain her!" The three men move quickly and grab the noble's limbs, forcing them behind her back and holding her in place.
"What is this?! Guards, remove them!" The command goes unheard, the techpriest having already hacked and shut down the estate's security system. The servitors remain in their hidden compartments, and a look of dismay flashes across the noble's normally well restrained complexion.
"Lyra Mae, you are no longer a recognized noble in this city, on this planet or even in this galaxy. You lost any power you had when you consorted with the ruinous ones." The female motions for her to be moved outside and the group walks through the halls, servants stopping and staring at the strange events taking place before them. Lyra Mae is forced through her own halls as a prisoner, struggling the entire time before forced out the door onto the bright green lawn of her estate, a large gold statue of the Emperor of Mankind the centerpiece of her grounds. How ironic.

She is placed before this statue and the men hold her in place as the Sororitas stands before them, reaching into her robes to produce a single weapon. Small, of strange design that seems if it were meant to be much bigger and was squished in the process of design, instantly recognized by all present; a bolt pistol. She pulls the slide back and chambers a bolt, glaring at the noble all the while.
"Lyra Mae, you are a Heretic and a Traitor to the Imperium of Man. Your crimes against the Emperor do not go unnoticed."
"You... you said the investigation was off... You lying *****...!"
"Do not interrupt me, Slaaneshi *****!" She fires off a single round which pierces the soft flesh of Lyra Mae's shin, rushing into the bone where it detonates, shearing her leg off below the knee with a scream of agony flying from the lips of its previous owner, blood pouring from the new wound and covering the gravel with a dark red pool. "With the Emperor as my witness, with the power bestowed upon me by the Imperial Inquisition, to uphold the Emperor of Mankind's law and to protect this world from taint, you are hereby sentenced to death." She fires another bolt, this one into the other leg and it too, explodes, the men dropping Lyra to the ground as she pathetically holds herself up by her arms, sobbing with pain as she attempts to look the Sister in the eye. "Have you any last words, Heretic?"
"I.... I never... I just wanted to..." She fumbles for words, the immense pain of having lost two limbs clouding her brain. "I was tricked..."
"You are now also guilty of lying to a member of the Imperial Inquisition." The Sister takes a few steps forward, reducing the distance between the two of them to less than a foot. She lowers her weapon so the barrel is aiming directly at the noble's forehead and glares. "The punishment for this is death as well."

"You have three seconds to make peace with the Emperor, Lyra. After that, you will see if your excuse was good enough."
"Artemis, I... I nev-" The trigger is pulled and the top half of Lyra Mae's head explodes in a shower of gore and bone, the brain shredded to pieces instantly. Blood sprays onto the Sister's robes from what little remains of the noble's lower jaw and stains them a dark red and the body falls back, coating the base of the statue with vital fluids. Artemis returns the pistol to its place inside her now bloodied robe and turns to the men who are standing at attention behind her.
"Burn it. All of it. Let nothing be spared."