The network of stone caverns sat beneath the rain-drenched cobbles of Knockturn Alley, quiet save for the steady trickle of water seeping down from the street above. Alone in the subterranean darkness and the silence, the caverns played host to a secret legacy of cold, clinical brutality. Had their presence been public knowledge among the Wizarding world, few would have dared to believe that such a place existed under order of the Ministry of Magic. In the eyes of those Ministry officials who ordered the creation of these underground chambers, the place and the activities which it housed were the very definition of a "necessary evil". Anyone entering the cavern might be surprised to see hanging from the ceiling the partially-dissected corpse of an adult Basilisk, or the mass of ethereal fungal strands which formed together into a disgusting womb around a squirming Dementor embryo. This was a place where the darkness was studied; where the powers of evil were collected, investigated and catalogued. In this hall of grotesqueries, a human - a mere Muggle - lay unconscious.

Within the darkness the captive awoke, one half of his face numb from where he had been laying in the thin layer of cold water which covered this patch of the floor. Cold and aching, the man struggled to sit upright, swiftly realising as he did so that his wrists and ankles were bound in chains. He blinked once, twice, trying to clear his vision. The dark blur which surrounded his eyes began to swim into focus, indistinct points of light revealing themselves to be a pair of flickering oil lamps above a heavy stone door. Sitting on the ground not far away from the captive, barely illuminated by the lamplight, was a steel tray whose contents betrayed the events which had preceded the captive's unconsciousness. Upon the tray there were a number of bottles of indistinct fluids - one labelled Veritaserum, among others - along with a silver crucifix and a .38 revolver which both belonged to the man. Staring at the otherwise unremarkable collection of items, the captive's memory started to slowly seep back to him. He remembered the interrogation which had taken up the last several hours of his life.

In the blackness behind the captive, what looked like wisps of thick, black smoke coalesced together and started to take form. In a matter of seconds, the strands of darkness had solidified into the shape of a tall, slender-bodied male, his face and upper body obscured by the shadows. In a couple of brisk strides he closed the distance to the captive, and idly kicked the man a good ten feet across the floor, sending him reeling into the nearest wall.
"My apologies", the newly-materialised individual spoke as if to nobody in particular, his accent the very model of Oxbridge English; "but we can't have you getting any dangerous ideas, can we?"
The captive squirmed in pain, sure that the brutal kick he had just received had ruptured something internal. Shaking the stars out of his vision, his eyes immediately went searching for the tray again...there it was, his revolver and crucifix still there. If he could summon up the strength for a lunge, he could possibly get his chained hands on the gun. A bullet between the eyes should certainly put an end to the heathen wizard who had conducted his interrogation.

From the end of the room, the stone door began to open with a groan. The grinding of mechanisms came to a halt as it opened just far enough for a businesslike wizard carrying a number of Ministry files to slip in through the gap. The sliver of light shining in from beyond the door seemed to burn all the more fiercely in the darkness of this cavern. The shadowy interrogator took a few steps towards the Ministry official, carefully avoiding where the light fell. As he stepped closer to the lamps, however, he became sufficiently illuminated to reveal his mode of dress; a black waistcoat and shirt underneath a burgundy leather long-coat. Coupled with his posture and voice, the overall effect was of some nightmarish parody of a Victorian surgeon. The Ministry official quickly flashed a Wizarding Intelligence Agency ID, and interrogator nodded, once. The Ministry official spoke, his voice careful and measured.
"You would be Mr Blake, yes? The analyst?"
"That would be correct. Am I to assume that the director has appointed you as my new handler?"
"I am your new liaison to the WIA, Mr Blake. I don't think there's any need for such an...antagonistic term for my position."
"I simply prefer not to mince words when dealing with fellow professionals. Now what do you have for me?"
The official paused briefly, glancing around the room at the various horrifying exhibits within. He felt himself suppressing a shudder at the site of the Dementor larvae growing on the ceiling.
"Erm...well, I see you have already begun work on the captive we sent you."
"I have. He is of the Brotherhood of the Light, or so he eventually confessed. He also said an awful lot of rather aggressive things about wizards in general. So who are they and what do they have to do with us?"
"They're an extremist branch of the Muggle Church, Mr Blake, a kind of modern-day Inquisition if you will. They've been burning American wizards and witches at the stake recently and naturally they need to be stopped. They pose an even more significant threat given that the Triwizard Tournament is being held at the Zephyrwit academy for the first time this year."
"I see..."
This time it was Blake who was silent for a moment, as he seemed to be considering something. Finally, he continued;
"So I presume that I am being assigned to the United States until this problem is addressed?"
"Indeed you are", the official replied hastily; "This file contains our intel so far on the Brotherhood, in addition to whatever you've learned from our unfortunate captive down there. It also gives you the address of a site close to the Zephyrwit grounds where you can Apparate to...don't worry, we've taken time zones into account so that if you leave in the next few hours you don't Apparate into the mid-day sunshine. A hotel room in New Oldtown has already been booked for you."
"How considerate of you..."
Blake's voice dripped with sarcasm at this last point; the official merely gave a polite cough, before handing over a second file.
"Once you've arrived, you are to find this individual and proceed from there."
Blake glanced over the file he had been given; one eyebrow raised quizzically.
"This is the Ministry's file on Jason Frost."
"Indeed it is."
"I was sent this file for analysis on three separate occasions over the past eighteen months. Each time I concluded that 'callous and over-zealous fanatic' might be the kindest description one could give him. 'Paranoid borderline sociopath' may be just as accurate. When I was told of his marriage to Madeline Pairis I concluded that she may indeed be a stabilising influence on his mind, but she's also an enormous target for his enemies. Losing her could push him over the edge from being a staunch enemy of the Dark Arts to one of its most ruthless champions."

Silence lingered in the cavern between the two men; evidently there was some tension in the air. Eventually, the official spoke up;
"Which I'm sure you have ascertained is part of the reason why we're having you observe him in the field. Aside from that, Frost is also an exceptionally competent WIA operative, regardless of your opinions of his psychology. You have your orders, Blake."
As the two men conversed, the captive was crawling silently on his belly towards the tray, and the gun which lay upon it. He could scarcely believe that these two magic-wielding heretics would stand and chatter idly while completely ignoring him. Pushing the pain out of his mind, the Brother of the Light lunged forwards and closed his hands upon the hilt of the revolver. Rolling once, he sighted his interrogator and squeezed the trigger three times. Three thunderclaps echoed through the cavern - had they been so arrogant as to not even unload the weapon?! - and three bullets slammed straight into Blake's chest, puncturing his heart.

Blake didn't so much as flinch. In a blur of movement so fast that the eye could barely register it, he was upon the gun-wielding captive. A scream resonated throughout the chamber as the captive's hand was twisted off at the wrist, sending the revolver clattering away across the floor, followed by a spray of arterial blood. The interrogator's hand clamped around the captive's throat, lifting him off the ground as if he were a paper doll.
"You can't kill me with that thing", Blake hissed, gesturing towards the dropped handgun; "I'm already dead."
For the first time, the captive was close enough to his tormentor to get a good look at his face. Blake's skin was ghastly pale in colour, his eyes tinged with bestial red, and a pair of lengthened fangs were visible in his mouth. In that instant, the Brother of the Light realised what this monster truly was. His realisation immediately became irrelevant as Blake's fangs tore into the captive's throat. Warm blood welled up into the vampire's mouth, and he drank hungrily. Erastes Blake rarely fed on human blood from a live vessel while in service to the Ministry, so the opportunity to now do so was relished. He bit deeper still, gulping down the copper-scented fluid like a man out of the desert dying of thirst. In seconds, the captive's body hung limp and bloodless. The vampire released his grip, and the corpse hit the ground with a dull thud. Slowly, he turned back towards the WIA official, who was staring in horrified fascination; it was clear that the man had never witnessed a vampire in the full throes of bloodlust before.

"I'm sorry you had to witness that", Blake said in a voice which carried not even the merest hint of being sorry; "Give me an hour or so to tie up loose ends and then I shall Apparate to the point detailed in the file. Thank you for your assistance thus far."
"Erm...yes...yes, you're welcome" mumbled the official to himself, before spinning swiftly back towards the doorway and making his exit. The heavy stone door ground to a close after him. The corner of Erastes' mouth twitched upwards into a smile of smug self-satisfaction as the official departed. Time for a trip to America, then...