Artemis was able to tell he was being followed as he approached his quarters. Even though they attempted to mask their sounds as Artemis's own, they were unskilled and gave themselves away in a million small ways.
However Artemis had to admit that he could see no shimmer or sign of his shadow, they were not using one of the more common spells for camouflage.

I wonder whether it is simply a clever student stalking me, one of the professors, or if I have misjudged Voldemort's resources and am currently being watched for signs of betrayal?

Artemis quickly debates himself about if it is wise to lead them to the rooms he and Filius share. But it is no great secret that they occupied this section of the castle, and would look suspicious if he turned away now.

Striding forward to the patch of wall that hides their rooms, Artemis takes no great trouble to hide the password. He will be most certainly changing it in a few hours.

Since the room beyond is carpeted in a soft blue material, Artemis steps lightly after he enters. He needs to be able to hear if the shadow follows him into the room, or stays behind.
As he hears their footfalls inside the room, he knows he will have to take action to discover their identity.

Crossing over to the small cupboard, he opens it out and briefly goes through his mental catalog of which bottles contain what substance, selecting the one that should gain him an advantage over his inept intruder.

Taking a good dose of the potion while still standing, Artemis experiences the expected blurring of vision, slight nausea, and an increase to the seeming brightness of the room. Then sitting down while he waits for the potion to work, Artemis attempts to focus on the bottle in front of him.
I am not looking forward to the side effects I will experience when this wears off.

Shortly afterwards, things snap back into focus, the colours and details of everything he sees much more clear than before. Trying to make it seem natural, Artemis glances up out of the corner of his eyes towards where he expects the intruder to be standing.

That is odd... This potion is supposed to be the best, and yet all I can see is a blurry, shifting form. It appears to be shaped like a cloth of some sort, draped over what I assume is a person. From the height, it is either a student or one of the shorter races. It appears to be behaving like an invisibility cloak similar to the one Foaly so thoughtfully provided me with. However I have tested this potion out on a variety of methods of hiding, my cloak included, and have never seen this effect before.

I can only assume that this is either a more powerful version of an invisibility cloak, or else a new item entirely. I see I still have quite a bit more research to do in this area of magic, if I already have encountered something new that I am not prepared for.
Thankfully there are other ways of identifying someone one cannot see.

After spending a few more seconds covertly observing the hidden person who seems to be shifting about uncomfortably and looking about the room. Artemis decides on a plan, as well as a few backup plans in case things turn out poorly.

Taking one last dose of the potion so that its effects will not wear off at an inopportune time leaving him vulnerable, Artemis carefully screws the lid back on the bottle of the potion that has turned out to be a bit of a disappointment.

Getting up, he knocks on Flitwick's door to let him know that he is back.

Filius quickly comes out, eager yet worried to hear how everything went.
"So, did things go well sir?" He asks.

"They vent," Artemis reply's dryly. "I have succeeded in gaining a few more allies, most notably the vampires, banshee's and satyr's. Talks have progressed further on a few more races. Sadly the surface fey have declined, and I have not managed to secure the giants. I doubt we shall miss their particular... charms."

Artemis does not mention details in front of the intruder. It would not do for them to learn exactly what he was asking these new allies to do, in exchange for various considerations.

Then in a lovely moment of pseudo acting, Artemis briefly allows some mostly real emotions to cross his face for the benefit of the silent watcher, and lets slip the news he hopes will get a reaction out of the intruder.

"There vas something unfortunately unexpected that occurred after my meeting with the vampires, but it might vork in our favor. I simply have to find a way to turn this to our advantage."

He then rolls up his left sleeve, keeping it angled away from the intruder so they have to move closer to see the mark upon it.

While Filius is horrified, Artemis keeps an eye on the intruder. As he watches them move closer, he rules out them being a minion of Voldemort since they would already know of the marking, and have no reason to want to see it close up. As the intruder gets into a position that they can see the mark from, they jerk back a bit, confirming that they had not suspected such a thing from Artemis.

Taking a deep breath, and noting any unusual scents upon the air that may be from the very close intruder, Artemis continues.
Filius asks a few questions and Artemis answers them openly. Since the intruder is likely opposing the Dark Lord, having them know that his joining was not voluntary should help gain their trust in the upcoming confrontation.

Then letting his robes sleeve roll down once again, he releases both observers from staring at the mark.

He assures Filius, "It cannot be undone. I simply have to plan around it from now on."

"But... what will you do if he asks you to kill for him, or torture for him?"

"Then I vill do it, and pretend to like it." Artemis replies in a flat voice, not giving away that he has already had to do some detestable things.

"However, this unfortunate turn of events simply means that I now have inside access. I can use this to find out his secrets, and then ve vill end this."

As Flitwick attempts to comfort Artemis, reaching out a hand towards him, Artemis quickly shakes off the hand and stands up, walking to the wall he entered by.

Time to end this, I think I have a excellent idea of who this intruder is now. If I am correct, then I could gain quite the advantage.

Artemis mutters the same password as before and inwardly grins, because honestly, what idiot would have the same password for entering as well as leaving.

The wall goes transparent and Artemis leaves, taking advantage of the brief time he will be out of direct sight of his shadow to ready his wand. Silently hoping that they take the bait of an apparent exit, he strides forward ten paces to make sure that he is out of reach of any direct physical attack.

Harry watches as Artemis walks away from him down the hall but something seems off, and it takes him a moment to figure out what it is. The hall being shorter than it is supposed to be is the first clue, and is quickly followed by the realization that none of the paintings seem to be moving like normal.

Then before Harry can figure out what it all means, Artemis whirls about and calmly says, "Incarcerous."

Before he can bring his wand up to defend himself, Harry is tied up with his invisibility cloak wrapped around him, and unable to move. He slowly starts to topple to the ground, losing his balance and hitting with a muffled "Oof" of pain.

Artemis quickly and efficiently proceeds to deprive him of his wand and bind him even further, before slowly walking back towards him.

"You didn't think it vould be that easy did you?"
Artemis smirks at the struggling prone form, "Oh and you are not actually in the hallvay, so don't expect any help to be vandering by anytime soon."

He then kneels and pulls the hood of the cloak off Harry's face.
"Ah, Potter, I thought it might be you. And how have you been over the vinter break?"

Furious, Harry spits out, "Like I'm gonna tell you, Death Eater! What do you even want with me? You wont get away with this!"

"Tisk tisk Harry. If I recall correctly, you are the one who vas caught spying on me. You should relax, I'm not going to hurt you. There is a chance you vill have to be obliviated, but that is entirely dependent on your co-operation."

Giving up his struggles to get free of the spelled ropes, Harry responds with a snort. "Hah, like I'm gonna believe that! You and Professor Flitwick are up to something, and it can't be good."

"You are partially correct Harry, Filius and I are indeed 'up to something' for ve are both agents of a foreign government.
Vhen you notified the vorld that the Dark Lord had returned, I vas called in to monitor the situation, as vell as try to find a discreet vay to end it before it could once again spiral out of control and threaten the government I work for.
I have no intention of harming you, since you could prove key to the Dark Lords undoing."

Harry thinks about this, and back to what he had overheard in the room.
Artemis was definitely a spy of some kind. He probably was not actually Russian, cus that would be too obvious. And it makes sense that other countries besides Britain would be interested in making sure Voldemort didn't get into power. Artemis could have just killed or kidnapped Harry at any time, but didn't.

So Harry looks hopeful as he says, "So then, you're here to help? But, you got turned into a death eater! How can I be sure you really are what you say you are? And why the bloody hell did you attack and tie me up if you are on my side!"

"Becoming a death eater was not my original plan," Artemis sneers.
"However it vill help accelerate my information gathering, even if it does expose me to greater risk. As for restraining you, I could not be sure you vould be a possible ally, so I had to be certain you vould not be able to attack or expose me."

Taking a moment to examine the material of Harry's cloak while talking to him, Artemis notes that it seems to be of slightly different material than normal, sadly there is no obvious reason for its advanced powers.

Artemis continues, "Incidentally, unless you are villing to swear an unbreakable vow to not reveal this information, I vill have to remove your memory of this.
The only reason I am villing to let you keep your current knowledge is that you can help me further my research into the Dark Lord.
You have one minute to decide."

As Harry thinks about it, Artemis takes a moment to congratulate himself.

This is turning out to be more fortuitous I thought! The boy surely knows more than he is aware of, and getting the details of his previous encounters with Voldemort could be a vital clue. Additionally, Potter can provide me with access to the Chamber of Secrets, which is possibly where Voldemort learned something that led to his current immortality. Who knows what treasures of information could lie hidden within that room.
I might even find... no... best not to get my hopes up. Slytherin was not exactly known for his spirituality.

I almost feel bad for Potter, he stands no chance at all. If he does not agree to the vow, I will simply wipe his memory to the point where he followed me out to this trap of a room, and try again with a new strategy.

But Harry finishes making his decision before the minute is up. "I'll only make the vow if you promise to tell me everything, and only tell me the truth! I am sick of being lied to, and having information withheld from me because 'I'm not ready for it'." He ends sarcastically.

"You are foolish if you think that I am free to tell you everything. I know the government I vork for would be highly displeased if all its secrets fell into a young boy's hands."
They certainly were displeased when it fell into mine! Hahaha... It seems it is true, I really am becoming more prone to joking as I age. Artemis thinks to himself.

"I vill only make you one concession, everything I tell you inside this room shall be the truth. I vill be villing to swear that I have not lied to you from the moment I tied you up. I vill make no guarantees about answering every question you have, and I am still free to lie to you outside this room."

Nodding his head slowly, Harry concedes that he probably can't get answers to everything. "Fine, but if you want me to help you more than just keeping quiet about you, then you'd better make sure to keep me informed, and do it in this room so I know you aren't lying to me!"

Artemis nods back, agreeing to the demand. Taking a risk, he removes the ropes and gives Harry back his wand so that the vow can be made. Luckily, his assessment of Harry wanting additional information more than revenge is correct, and there is no sudden attack.

The vow is made, and Harry immediately explodes into questions.

"So, tell me everything you are able to tell me! I want to know as much as I can.
Is this why you were teaching me and my friends to fight better? Do you know why Voldemort keeps attacking me? What government do you work for? What are you trying to learn here? Why are you recruiting Vampires and Banshees?" Harry quickly stops as Artemis grimaces in pain and hold up his hand for quiet.

"I cannot answer you if you vill not stop talking..." He remarks with obvious impatience.

Leaning up against the wall so he will not lose his balance now that his vision is gone due to the potion he drank earlier, Artemis continues talking.

"I am teaching you and your friends partly to get closer to you, and partly because anyone who has been attacked as much as you have really should know something about defending themselves. Your past teachers have been idiots.

I have my suspicious about vhy you are a target for the Dark Lords ire, but vithout knowing the details about each time he has attempted to harm you, I cannot be certain.

As for vhat I am attempting to learn here in Hogvarts, there are many things, but chief amongst them are possible methods of immortality and how to defeat them. It is clear to me that vithout defeating his current safeguards, any attempts to end the Dark Lords life vould be futile."

At this, Harry makes a few noises of protest, "But, he can't really be immortal, can he? I thought that was impossible? Even the Philosopher's Stone just extends life and restores youth!"

Artemis is disappointed to note that Harry sounds shocked by the idea that Voldemort is currently unkillable.

Why am I disappointed? He thinks. These wizards seem to lack even the common sense that regular people have. Perhaps magic stunts the brain development of humans? I shall have to look into that later...

"Da, I do believe that he cannot currently be killed, not in any permanent fashion. Now if you truly vant to help me, you could tell me about each and every time you have encountered him, and vhat occurred. I understand that every year at Hogvarts has been eventful in some vay for you?"

Harry proceeds to hesitantly tell Artemis about Quirrel and the Philosophers Stone, the Basilisk and the Diary, and the end of the Triwizard Tournament.

At the end of the re-telling, Artemis's mind is a-whirl with possibility's and new ideas. Although I do wonder what happened that year with Sirus Black escaping, since it seems that it was not at all related to the Dark Lord, if Potter has not mentioned it along with the other incidents.

"I have much to think about, it vill take me a bit of time to draw any solid conclusions." He explains to the boy who is likely fidgeting in impatience by now.

"In one veeks time ve shall meet again. If you are villing to open the vay for me, then ve shall go into the Chamber of Secrets and seek any clues that might have been left behind by the Dark Lord. I vill in payment share vith you a few hypotheses based on the information you have just provided me.
Does that sound acceptable to you?"

"Yeah, that sounds ok. Uh, will we still be getting private defense lessons from you?" Harry asks with a suspicious sounding tone.

"Da, although once your group masters a few certain spells, such as the Patronus and a powerful healing spell called Sarcirent, things vill change. I plan on opening up the group to anyone who wishes to join, and setting you all to teaching them vhat you have just learned."

Harry sounds baffled, "Err, why? I thought you didn't want to risk teaching a large group? And how is us helping teaching people going to make us any better at fighting?"

"Simple. First I believe I have found a vay to teach everyone vithout Umbridge's interference. There is no guarantee that ve vill be able to resolve this situation with the Dark Lord quickly, and this should prove important to my long term plans.
Secondly, you vould be amazed at how much you can learn by teaching someone."

Straightening up from his lean against the wall, Artemis carefully walks towards where he remembers the doorway to be, hoping that his current blindness is not obvious.

After-all, it would ruin the effect of the 'powerful all knowing spy' if I were to stumble or walk into the wall. He jokes to himself. I need a better method of seeing though disguises for next time. This one is not adequate. Temporary blindness as a side effect is annoying and only worth it if the potion works.

"Hide once again, then follow me out. I vill let you out correctly this time, you may then go back to your usual habits." He tells Harry.

Calling out to the wall in Gnomish, Artemis can hear the slight whoosh as the air from the two rooms begin to mix.

Stepping through, he waits for Harry to arrive behind him, before he gently speaks the proper phrase for leaving. His mind is a-whirl with concern for how the events of the past few years are going to change his plans.

Harry quietly says, "Thanks."
As he leaves, he startles Artemis by touching him on the shoulder briefly before he is gone.

I wonder what prompted that? No matter, I have an immense amount of work to do. Not to mention starting myself on some exposure therapy for the PTSD that is manifesting from that oh so lovely time spent with Voldemort. He thinks sarcastically.