Disclaimer; As usual I don't own Harry Potter or it's associated characters, but here's another thousand words or so of Omerta.
Finding a second invisibility cloak had not been easy, but it had definitely been worth it, Harry reflected as he and his "apprentice" stalked through the dungeons. Dexter was a vicious little sociopath, but he still needed a bit of training on the finer points of sneaking around. The young Ravenclaw halfblood had only been at the school for a few months but was already on the brink of expulsion for his tendency to start fights over every perceived slight. Their mission in the dungeons tonight was to send one last warning to certain elements in Slytherin house.
The week before one of the students under his protection was threatened that she should "respect her betters" now that the Ministry had finally acknowledged Voldemort's return. It was a pretty weak threat, after all it was unlikely the Dark Lord would care about schoolyard slights, but Harry wasn't about to let such obvious attempts at inspiring terror go unanswered.
His little "study group" had started with people looking to him for protection, but it didn't take much to prod them into other areas as well. They were up to twenty students above fourth year and alumni now and it wouldn't be long before those twenty owned Hogwarts from the student side. Hufflepuff loyalty and Ravenclaw strategy were truly scary when combined. Sure it may not be important in the grand scheme of things but it would definitely help to have a system in place to recruit young wizards with interesting skills and it would give them practice for the kinds of machinations that would help them in the real world. His little jaunts with Dexter were just one such training mission.
Harry stuck one hand out from under his cloak and waved for Dexter to hurry as he could hear his footsteps lagging behind. It wouldn't do to be late and miss their chance to get into the Slytherin common room. One of their two Slytherin members would be leaving the common room precisely at half past eleven and if they missed their entrance they would have to reschedule the retribution.
They arrived right on time and Harry gave their Slytherin member a touch on the wrist to know they were past. The two invisible students split up and prepared for their attack. Three Raveclaws had worked for most of the last week to prepare the warning they were here to deliver. As he circled around behind Nott, Harry pulled one of the enchanted dagger hilts they made and activated it. Instead of a blade, these weapons only had a sticking charm and a stunning spell applied to the crosspiece.
At the stroke of midnight, Harry swept forward with one hand over Nott's mouth and planted the surrogate knife right between his shoulder blades. His eyes flashed red before he lost consciousness and fell to the floor. Already moving, Harry slammed the next bladeless dagger into Zabini's gut. Across the room Harry could hear a shrill war cry from Dexter as Malfoy suddenly sprouted a knife from the middle of his forehead and was knocked violently onto his ass. Harry made a note to explain subtlety to the boy later.
Needless to say, the rest of the house went apeshit. When one of the prefects ran screaming from the common room to get the professors, Harry and Dexter slipped out the open door. Aside from the three boys who had been "killed", there were only three other clues to who was responsible. In the sixth year boy's dorm, a gift was found on each of their beds.
Inside each was the blade to the dagger that had stunned them and a simple warning. "Respect your betters."
Despite the fact that Harry was skimming a healthy percentage of his group's ill gotten gains off the top every week, he wasn't actually making all that much from running his little club. With his knowledge of the castle's hidden passages and secrets he was able to vastly increase the flow of certain contraband within the castle. While porn, booze, and other necessities of teenage life were always in demand, his real money was ironically enough coming from potions. It was an unwritten law that students couldn't buy certain potions or the key ingredients, most notably memory and intelligence enhancing potions for students in their OWL or NEWT years. By starting to supply the needs of the masses early he avoided the wrath of the professors that would surely appear as examines grew closer.
With their alumni contingent (strangely not including the Weasley Twins) helping it was fairly easy to line up a steady supply and his people were making a killing. Harry however was everybody's friend, and his cut went right back into their pockets in the form of gifts, services and other loyalty building exercises. He even splurged a bit from the Black family funds to get one of his potion supplying alumni the services of a veela hooker.
Once they were secure in their position as the top distribution network in Hogwarts, they moved on to running numbers and on the insistence of their Slytherin contingent information brokering. The latter was immediately seized by the Ravenclaws as an excellent alternative to giving away their tricks along with a dose of preaching and humble pie as they had in the past. Soon it was common knowledge that if you had a problem, you could ask one of the brokers and for a price, not always in cash, they'd solve it.
By the time winter holidays came around, they had recruited a few more recent graduates and started to compile long term plans. All it took was for Harry to muse aloud about what it would take to establish a real presence in Diagon or Hogsmeade and the whispers began. The ideas he saw spawned in the next hour were nothing short of astounding. The Brotherhood of the Eyrie was born.