Hermione had already returned to her dormitory. What they were about to do was unknown: perhaps nothing would happen, or perhaps there would be unforeseen dangers. Naturally, Su Er had persuaded Hermione to return to the common room for now.
Su Er promised that if everything went smoothly, he would come and tell Hermione right away.
After leaving the Headmaster's Office, Su Er, under the Disillusionment Charm, led Dumbledore to the Room of Requirement, entering a room filled with all sorts of miscellaneous objects.
This was also the hiding place of Ravenclaw's Diadem, one of His Highness Braised Egg's seven Horcruxes.
"Lumos."
A ball of light as bright as a little sun floated above their heads. Following the movements of Su Er's wand, it illuminated a narrow path between mound after mound of piled-up clutter.
They passed a mound of broken mirrors and went around a towering wall of assorted rusty armor. As they passed a mound made up of all kinds of books, Dumbledore suddenly stopped, looking intrigued, and gently raised his hand.
With a rustling sound, the mound of books shook and floated into the air, forming a long dragon.
Dumbledore looked up, his eyes flickering. With a slight movement of his slender fingers, dozens of books flew out of the dragon made of books and arranged themselves in rows before him.
"An unexpected find." Dumbledore chuckled. A cloth bag appeared in his other hand, its mouth opening, and the books jumped into it one after another like soldiers.
Under Su Er's somewhat puzzled gaze, Dumbledore explained quietly.
"Some books missing from the Library. I didn't expect to find them here. This has nothing to do with our purpose here; I simply happened to notice them. Madam Pince will be very pleased to see them returned to the