The eerie feeling of the room. The color of it. Its bleakness. You think you're about to be questioned. You don't even know why you are here, but you think you're going to be instigated, of some sort.
Allow me to provide you with some calming thoughts.
You are not here to be questioned, or for lack of a better word, punished. Two years ago, you appealed to the Domestic Security Committee for a chance to work in a better division, compared to what you have now. As you know, you never received any actual answer to your request, until now.
I am Haydrick Barnes, a special agent for internal security. You may call me by my last name. However, if you ever do meet me again outside of this room, you won't be calling me that in public or in private, which I will address at the end of this. You are here because my department has had a keen interest in your skills since you've first joined the Foundation. Your ability to make effective judgement in sudden scenarios, impervious to forms of bias or partiality, and overall proficiency within the intelligence and documentary fields of the Foundation, have made you a reliable candidate for the Internal Security Department.
You look confused. Surely, you should have been able to deduce that there must have been a controlling factor in what you're able to see and do here. A lot of people like to assume that the department doesn't exist. I am assuming that you've heard the rumor of a 'foundation inside the Foundation'. We, ourselves, don't mind the idea that people think the department is only a myth, because it provides us with the perfect cover for any operation we commence, internal or external. It also provides us with a reliable connection directly with O5 Command, and notable members of Site Command, should the need to ever contact them arise.
Let me ask you a question. How do you think the Foundation keeps track of everything that happens? How do you think they keep track of the information that was gathered? Keep in mind that we only have less than a hundred Site Directors, and only thirteen members of O5 Command. I don't think the administration, consisting of only a few intellectually gifted individuals, would be able to account for everything that transpires, or around the world in other designated sites.
That is where we come in. That is what the job of an internal agent.
More often than not, you'll find at least one or two among a hundred Foundation personnel trying to do something that would slip right past the 'all-seeing-eye' of the O5 Command. That means that they've also managed to bypass the administration and or RAISA, as well. However, we're not responsible for what happens during an information breach. We're responsible for what happens before and after it.
Repeat the question? No, we aren't responsible for the classification of documents. However, we do hold the jurisdiction to make changes to any official Foundation document or report, however necessary. That being said, document classification and encoding is not our primary job. However, you will find yourselves in situations where orders from ISD will conflict with those from RAISA, which will more than often require a firm debate between both department directors or other supervisory agents.
Before I continue with the rest of the orientation, I'd like to ask you another question. Do you know who Aaron Siegel is? Yes? Good. Do you know why or how he disappeared? No? I see. That means that you haven't picked up the letter yet. However, you must be wondering how he disappeared. I'm going to ask once that you take notes, because some of what I am about to tell you will intertwine with what you will be doing within the department.
Aaron Siegel served among the O5 Council, designated as 'O5-5', and tasked with oversight of the Intelligence Community; a large Foundation bureau tasked with securing and maintaining any and all information about— but not limited to— abnormalities, personnel, and foreign groups of interest.
He was one of the founders responsible for the creation of the Foundation, and also one of the first few O5 Councilors. During the early dawn of the Foundation, he was responsible for the documentation, record-keeping, and distributive properties of everything contained within the Foundation, and other important information.
Before his disappearance, he wrote another letter and gave it to one of his coordinators, which has been passed down from one ISD director to the next. The current director was kind enough to provide me with the letter for me to read off of, which is what I've had in my hands for a while now.

To my Intelligence Coordinator,
█████,
Everything that I have foreseen has come to fruition, and the conclusion we reached has been proven true. The Council is slowly deteriorating from within, and is therefore affecting the Foundation. I understand that this week has been hectic for you, but I am prepared to offer you a promotion to O5, should you choose to accept it. I've already spoken with the Administrator and O5-Head, and they are in full support. The reason I am doing this is because I will no longer be an active member of the Council, let alone the Foundation.
I am disassembling the Intelligence Community as soon as possible. And yes, I know what you're thinking. How I'm not in my authority to declare such, or for lack of a better word, ultra vires. Like I said, I've spoken with the Administrator and O5-Head. Everything I am doing and about to do has been pre-approved. However, clarification aside, I have reason to believe that with the Council's compromise, the Intelligence Community would definitely be affected as well. Therefore, the Intelligence Community will be delegated across three separate departments to avoid further damage:

Intelligence Agency, IA, tasked with maintaining information and coordinating external affairs operations and efforts with the Department of External Affairs, and other classified tasks outside of the Foundation.
Records and Information Security Administration, RAISA, tasked with storing and maintaining information, official documents, records and information, classification, and archives.
Internal Security Department, ISD, tasked with enforcing Foundation ordinances, policies, and laws of the Foundation, while operating incognito investigations of corruption/collusion allegations, ensuring information security and integrity within the Foundation. Additional tasks will be discussed to you when we meet at Site-██ tomorrow, for one last time.

I've already assigned who goes to where, and who will be directing those departments. The Administrator has offered you complete control and protection for any decision you make in regards to those agencies, praeter the O5 Council's decisions over those agencies as a whole. The O5-Head, however, is expecting that all of the protocols, structures, and regulations, be set for all of them before the end of the year.
Setting up IA and RAISA won't be an issue. I know that for a fact. It's ISD that I am worried about. It was a controversial decision to even consider the creation of the IC's Information & Enforcement Sub-bureau, which is now being succeeded by ISD, and made into its own separate entity with almost infinite authority. I have no doubt that a structure and proper protocol can be determined, but I am worried about how ISD will be presented, who controls it, and who will represent it.
I sent you an email over the secured IC network, which includes a list of contingency protocols you can use in case things go down hill. In that list, I've also included names of people you can use for ISD's staff. You can refer to that list whenever you wish to. As for recruitment methods, department codes, and other necessary doctrines, I'd recommend contacting O5-██, O5-█, the O5-Head, and the ISD Director, for reference material or advice.
I wish you luck, █████. Continue the line of secrecy and integrity where I cannot.
Ab origine,

THIS MESSAGE WAS FROM THE EXECUTIVE OFFICE OF 'O5-5'
Secure. Contain. Protect.

If you're confused in any of this, allow me to help you recalibrate.
Aaron was among the first generation of O5s, if not, the first five. He was also the last person among the founders whom continued actively serving in the Council for years to come, and was the only one remaining when everyone else had left. This means that whatever he predicted, whenever he predicted it, has already happened, and is only getting worse.
That being said, Aaron didn't disappear. He merged with the living embodiment of the Foundation itself; he became the body and the soul of the Foundation. Ever-present, virtually immortal. Everything the Foundation has ever contained, is containing, and ever will contain, is known only by Aaron himself, and therefore, the intelligence apparatuses. He erased himself from existence, and in the process, was made into a martyr.
Our task,— and now yours,— is to secure the order that was kept in place for decades. To contain the protection of both our security and information. To protect the continuation that is the SCP Foundation.
It's not rocket science when trying to figure out how all this corruption, nonsense, and noncompliance to basic Foundation policy, managed to implant itself within the Foundation, and especially among us, above others. And when this happens, everything else is affected with it. Containment Procedures, official documents, reports, divisions, site command, assistant staff, all the way up to even the O5-Head himself, could be compromised to this man-made disease, if they are not compromised already.
The Internal Security Department was made for the sole intention of preserving and maintaining the order of the Foundation's cause and existence. It was made for the sole intention of preserving everything that Aaron and Administrator had created, and therefore, that the Foundation has created. We are our own embodiment of the Foundation; of those who seek prosperity, justice, and order, among the chaos. We are the will of the Foundation.
At the end of the day, that is our job. We are the roots of the Foundation. They cannot, and will not, be pulled from beneath us. You understand this now, don't you?

...

You're uncertain. Let me re-explain your position here.
Your job is important. You are important. They may not understand it, and you might not even understand it. But I do. This is where your story begins, and it will be where it ends; wrapped in a cold embrace, and never let go.
What you just read, which was not intended for you, was made to last for generations to come. It was not meant to be kept a secret, because nothing can ever be kept in the dark forever. The Foundation is compromised, and there is nothing that anyone or anything can do about it. Not the Council, not the Intelligence Community, and not you.
However, do not let that interject with your intentions or moral. Because while the Foundation may be losing its grip, you will not. Internal Security may cease to exist— and therefore the Foundation— but you will not. You were not raised like the rest of them. You were not manipulated. You are aware of your surroundings. Like an eagle on the hunt, you know where to look.
While the intelligence community manages to barely hold on to itself, as the mindset of human nature begin to corrupt their morals, you will hold on. You are armed with both sword & shield, and you— and only you— are given the leisure to determine when and how you use either.
You were born to serve humanity, yet you will find no humanity here. Not here, not there, not anywhere. Only criminals, sadists, and freaks of nature roam the surface. You are among the first generation of outcasts. You listen to the outside, where others are blissful within their own ignorance and incompliance to common sense and law.
You could be the key to all of this chaos, or not. Regardless, your actions and intentions have brought you to where you are today. You cannot fix what cannot be undone, but you most certainly can prevent more damage from ever occurring. You can put an end to the nonsense. Only your will, morals, and dedication, will drive you forward, and the Foundation will move with you.
You are here because I have confidence in your abilities. You are my creation. You are here because I willed it.
There is no coincidence. There is destiny; and your destiny is my will, and mine alone.
…

I'm glad we're of the same mind.
That being said, let me give you a full in-depth explanation as to what you will be doing in the department, and how you will be doing it.
First of all, everything that is discussed here and forever more about, similar to, or directly from or to ISD, is highly classified. You should know that by now without me having to explain what I mean by this, especially what would happen to you if you leak anything.
Simply so, if anyone asks you about ISD and is not currently aware of its operations to your own knowledge, simply respond with something generic; what other people would say to that. However, if someone consistently approaches you about the department, avoid general contact with the individual, and report it to the ISD's Apprehensive Interrogation Unit, and they will handle it from there.
In terms of general handling of information or operations, you will be trained how to handle information, what you need to do if you ever encounter Reality Benders or any powerful reality-bending sentinel, and more importantly, how to properly interrogate someone. An ISD Agent's job will mostly involve interrogations. Lots of them. That includes how to properly write reports, documents, classification methods and practices, and a longer list which I personally do not feel I have the time to recite.
In conclusion, the answer to a two-year question of yours has finally been answered. The Internal Security Department is willing to add you among its ranks.
Welcome to the brain.