Harry gritted his teeth as he searched for that blasted diadem. He had been at this for nearly two months now. Because of the memories he had accessed when he saw the diary and Hufflepuff's Cup, he was able to know the location of the other Horcruxes. Ravenclaw's diadem was here somewhere in the Room of Requirement. The ring was placed in the shack that once belonged to the Gaunts, but Harry had no idea where the hell that was. Slytherin's locket was in a cave, the location of which Harry didn't know. It was turning out to be frustrating because the room here was so huge that it was difficult to locate the diadem!
Turning into his Animagus form, the golden eagle soared above the junk, occasionally landing on something so that he could observe. It had been a week since the Death Eaters had escaped Azkaban and Harry was on edge. The reason was twofold - one, the Death Eaters were out there, especially Bellatrix who would love to get her hands on the Boy-Who-Lived. Two, there were a bloody hundred Dementors outside Hogwarts castle.
Harry hated the Dementors. The day after they had arrived, when Harry had gone for his usual morning run, he felt something he had never felt before. The cold was horrible and the grounds were dark. He could feel the negative emotions in the air, making him miserable. Bad memories resurfaced but thanks to his Occlumency, he was able to shield himself long enough to get back to the castle. He had since been working out in the Room every morning along with practising the Patronus Charm after having been explained the theory by his Aunt Amelia. Merlin knows he didn't want to be defenceless with those beasts around.
Flying back to the ground, the eagle transformed back into a human as Harry used the point me spell again. He had done this so many times that he felt like burning the entire place with Fiendfyre and be done with it! But he couldn't do that. For one, there were some really good treasures here that he was quietly shipping off to Potter Castle using his elves. Really, no one was going to miss it. Another point me spell showed the bust of an ugly witch with a diadem on it. Another memory slammed into his mind.
He laughed loudly as he removed the diadem of Rowena Ravenclaw from under the tree stump in Albania. Stupid Helena; did the ghost really think he would help her and return it to Hogwarts as a lost treasure? Never! He was Lord Voldemort. It belonged to him and him alone. He would turn it into a Horcrux at the first available opportunity. Then, it would be returned home. He would place the diadem in the one place he was confident no one other than him knew about at Hogwarts; right under Dumbledore's crooked nose.
Harry gasped as he came out of the memory. This was the Horcrux. Levitating it from on top of the bust, he asked the Room to change. The surroundings shimmered and a ritual room appeared with a book on a pedestal. Harry smirked. This was the ritual he and Sirius had found in the Potter library - an ancient cleansing ritual that got rid of the taint of dark magic on any device. It would not get rid of the Horcrux, but it would take care of any lingering dark magic to make the diadem taint-free.
Harry placed the diadem on the ground. Pointing his wand at the item, he summoned all the hatred he could muster.
His eyes were an eerie blackish-green as he snarled, " Avada Kedavra! "
A jet of pale green light impacted the diadem, making it wobble and scream loudly. After it stopped moving, Harry checked the diadem for the soul piece using the spell which Sirius had found in the book of Scorpius Black III. It had been destroyed.
Levitating the diadem to the ritual pentagram, Harry began chanting the words in ancient Greek as he walked around the diadem. Fifteen minutes of chanting later, he found the diadem to be red hot. With a final incantation, he swished his wand, pouring water on it. Slowly picking up the diadem, he scanned it. From what he could tell, there were no more additional spells cast aside from what Rowena cast herself. Swallowing his nervousness, he placed the diadem on his head and closed his eyes.
One hour later, Harry's lips curved into a smile. "Lady Rowena, you were a genius," he whispered to himself. The diadem innocently glinted under the light from the fireplace.
The diadem of Ravenclaw did not bestow the wearer with superior intelligence. It actually worked on a more fundamental principle in that it allowed the wearer to remember everything he had in his mind - an artificial eidetic memory. Harry, being a natural Occlumens already possessed a perfect recall memory, but he had been unable to access Voldemort's memories which were in his mind. He had only gained the passive abilities from those memories, helping him with his practical application of magic, making it much easier for him to learn it in the process.
But now, thanks to the diadem, Harry was able to access all of Voldemort's memories which were in his mind. He would truly learn from the Dark Lord like a student would from a teacher by viewing the memories. He would be the Dark Lord's equal, even if would take some time and a lot of effort.
Most importantly, as he accessed more memories, he would be able to know the location and defences of the rest of the Horcruxes.