Disclaimer: I own all seven Harry Potter books, but not the franchise. I'm getting that for Christmas next year.
A/N: This is not canon after Chamber of Secrets.
He opens the door and walks inside. The trapdoor is still there, although no dog guards it. He drops through it and lands in the withered remnants of a Devil's Snare- the original is now in Greenhouse Three, but a few limp vines remain. He walks through the Key Room's open door, across the abandoned chessboard, and through the Troll Room, as he dubbed it. It still retains that god awful smell, even though the troll is long gone. No fire springs up around him in the Logic Room, and he is there. The mirror stands in the center of the room, just as he remembers. No cloth covers it; no possessed professor blocks his view. He peers into its depths, wondering what he'll see this time.
A boy, eleven years old, with black hair and green eyes, sits on a stool at the front of the Great Hall; he's being Sorted. The Sorting Hat yells out a House; the word "Gryffindor" is easy to make out. The boy runs over to the table of red and gold. The scene freezes as the boy sits next to a ginger haired boy with a friendly smile and the next student is called to be Sorted.
He recognizes the boy; he's younger than the memory that came out of the diary, but still clearly Tom Riddle. He knows immediately what it means. He wants things to have turned out differently. If Tom Riddle had been a Gryffindor, Voldemort would never have been born; all his problems would have been solved, all the drama would never have happened… He smiles ruefully and shakes his head. If it had never happened, he wouldn't be who he is, and that's not something he's willing to change. He conjures a cloth to drape over the mirror, then turns and walks away. It is, after all, he thinks, just a mirror.