Per 
The hallway he was walking down did not look out of the ordinary at all. It was just a normal hallway that occupied the floor of a random insignificant site owned by the Foundation. There was nothing too suspicious about it.
However, the man in a Foundation lab coat was not concerned about the inconspicuous hallway. He had another objective in mind.
Walking at a brisk pace, he stopped in front of a door in the hallway. The ominous words 'QUARANTINE ZONE. DO NOT ENTER.' were written in red on the sign haphazardly stuck on the door. The warning was simple, but he knew that it was still an effective way to deter any unsuspecting researchers and janitors. After all, if one worked at the Foundation, they would have to be conscious about everything they interacted with.
Seemingly undeterred by the warning, he knelt down, pulled out an ID belonging to a person named 'Walter Martinez' from his coat pocket, and slipped it into the crack of the door.
He heard a rustling noise coming from behind the door and saw the card being picked up by a white-gloved hand. After a few seconds of silence, there was a clicking noise and the door that had supposedly led to a quarantined zone opened.
In front of the man in the coat was a black-suited figure adorned with a top hat and a mask that reminded him of the Japanese ogres, or oni, in folk tales. The black suit worn by the figure had done a good job in hiding their body lines, so the man could not tell if they were a male or a female. Overall, the figure exuded a sense of professionalism and mystery that he could feel.
The figure spoke in a whisper.
"Are you alone?"
"Yes," the man replied almost immediately.
"Does anyone know where you are?"
"No."
"Do you know who the Cleaners are?"
"I have never heard of them before."
"Did you bring any weapons?"
The man turned out his pockets. Sure enough, there was nothing.
"Good," the figure nodded before they took a step back and pointed behind them to a rusted, dark staircase that led down to inky blackness.
"You go through there. Do not turn back. Only go forward. The Seller will receive you at the bottom."
The man nodded and walked through the door towards the staircase. As the figure bowed and held out his arms in a pose eerily resembling a butler working at a fancy mansion, he adjusted the long sleeve of his coat, held on to the rusted railing and slowly descended down the steps, down into the inky blackness.
As he descended further down the staircase, he could see a dim light growing brighter and brighter at the bottom. As he got closer to the source of the light, he could see that it belonged to an oil lamp hanging on the wall by a nail. Similar more lamps lined the walls as he descended further and further down.
Another masked figure, this time with the distinctive bodylines of a man, greeted him at the bottom of the staircase.
"Mr. Martinez. I have been expecting you," the figure spoke with a slick, gentlemanly voice when he reached the bottom of the staircase.
"I assume you are the Seller, then?" the man replied.
"Yesss, that is correct," the Seller replied with a hiss, "I sell stuff. That makes me the seller."
"What sort of stuff do you sell then?" the man said as he surveyed the room the two of them were standing in. In the far, dimly-lit corner of the room, he could see a table stacked with different items in all different shapes and sizes.
"All ssssorts of stuff. High-level key cards, MTF weapons, important documents. I have even come into the acquisssition of some rare useful anomalous items. They won't bring you harm, I can assssure you that."
"But isn't most of this stuff illegal?"
"Yesss, but it isn't illegal if we don't get caught. The Cleaners," the Seller clicked his tongue in anger as he spat out the word, "they are irritating for sure, but as long as we are careful, we will not get caught."
"Right."
"So what is it you want, huh? I have heard from Mr. B that you have been very interested in my stuff."
The man adjusted his sleeve again and walked over to the table.
"There sure are a lot of…interesting stuff," he remarked as he surveyed an intrisically-crafted wooden disc that faintly glowed in the dim light.
"All from the very besssst source, Mr. Martinez."
"And you're sure you won't get caught stealing anomalous stuff from under the Council's nose?"
Silence fell. The Seller narrowed his eyes and eyed the man warily.
"You are Dr. Walter Martinez, aren't you?"
The silence persisted as the man turned around and pulled out a loaded Foundation standard-issue pistol from his sleeve.
"No, sadly not."
With a deafening crash, the quarantine door above them burst open, and several operatives armed with weapons rushed down the staircase.
"…how long have you known?"
The man ignored the Seller's question. In a firm tone, he remarked, "Dr. Timothy Williams, you are under arrest for the illegal possession and sale of anomalous items. For your sake, I highly suggest you surrender."
The Seller did not move, even as the operatives, who were dressed in all black armored suits, swarmed into the room and handcuffed him.
It was only when he was escorted out of the room that he spat out the words, "Fucking Cleaners."
As the man who had been wearing a lab coat and who was now in a black armored suit watched the operatives carry off the illegal items, he muttered to himself,
"One down, six to go."
In another room below another site, a meeting was being held.
"The Seller is down."
"I know that, Silencer. You don't have to update me on everything."
Various figures, both male and female, were sitting beside a round wooden table and arguing loudly.
"What do we do?"
"We listen to me! We'll take action against the Cleaners! Just like what we did with the new recruits!"
In the midst of the arguing, one of the figures sat in silence. Eventually, he raised his hand.
"Everyone quiet! The King is speaking!"
Everyone fell silent as the figure known as the King lowered his hand.
"The Foundation has long had its dark side. Missing items, mysterious incidents with seemingly no direct cause, even for some containment breaches, we all had had some part to play in those," he clasped his hands together and spoke, "but we haven't made ourselves well known yet. Well, we have waited long enough. It is time for us to bring the cards on the table. To make ourselves known. We will rain chaos."
Standing up abruptly, he pounded his fist on the table and declared, "The new dark age of the Foundation has begun."
As the cheers and screams rang out in the meeting room, the King smiled.
"Let the hunt begin."
