Astoria sensed Jon's mood shift. Seeing how distracted he became after hearing Professor Trelawney's account, she chose to leave the Headmaster's Office of her own accord.
After she descended the spiral staircase, Jon Hart—still seated in the Headmaster's chair—suddenly lifted his head. A sharp, resolute gleam flashed in his eyes.
"Phineas," he ordered quietly, "please contact Severus. We'll meet in front of the Potions classroom in ten minutes."
"Understood, Jon!" Headmaster Phineas Black, unusually serious and without his customary levity, nodded solemnly before vanishing from his portrait.
"Should we call anyone else?" Headmaster Dexter Fortescue asked with concern from another frame. "If it's only you and Severus…"
"No need," Jon replied with a small shake of his head.
He took a sip of Polyjuice Potion from the teapot, then tucked Albus Dumbledore's Elder Wand into his belt. Without hesitation, he strode down the spiral staircase and left the Headmaster's Office.
...
When Headmaster Albus Dumbledore arrived at the Potions classroom in the castle basement, Professor of Defense Against the Dark Arts Severus Snape was already waiting.
The two exchanged nothing more than a glance.
Then their eyes shifted in unison toward the Potions office ahead.
Dumbledore stepped forward and knocked lightly on the office door. Snape, meanwhile, moved soundlessly to the side, blending into the shadows along the wall.
"Who is it?" came Horace Slughorn's lazy voice from within.
"It's me, Horace," Dumbledore replied evenly.
"Ah, Albus… You haven't come to see me once since I was discharged from St. Mungo's… What delightful thing have you brought me this time—"
His hearty tone cut off abruptly.
The moment he opened the door, he found Dumbledore's unmistakable Elder Wand pointed directly at him.
"I… don't quite understand… Albus…" he stammered.
"I believe the masquerade has come to an end, Horace," Dumbledore said with a faint smile, holding his wand steady without casting a spell.
"What masquerade…" Slughorn muttered, his right hand inching subtly toward his own wand—
"Expelliarmus!"
The cold incantation rang out from the side.
Severus Snape stepped from the shadows and neatly disarmed Slughorn, seizing his wand.
"Oh… well…" Slughorn let out a short laugh, sounding oddly relieved. "Severus, you're here too. Good evening! Albus, there's no need for Legilimency or Veritaserum… I'll confess. From the very beginning. I'll tell you everything."
...
Snape cast Dumbledore a puzzled glance. This was going far more smoothly than either of them had expected.
The bald, portly old man shuffled back into his office and collapsed heavily into his reclining chair.
"How did you find me out?" he asked gruffly.
"Well," Dumbledore replied lightly, "you left rather too many loose ends, Horace. And quite unfortunately for you, just a few days ago, one of your associates betrayed you."
Slughorn slapped his broad forehead with his plump hand and nodded thoughtfully.
"So tell me, Horace," Dumbledore continued, his tone almost conversational, "did I invite you to teach at Hogwarts before Tom asked you to become a Death Eater? Or was it the other way around?"
"Of course I agreed to return to Hogwarts first," Slughorn answered without hesitation. "I was simply unlucky. Three days after giving you my word, a former student came to visit me… and as it happened, Death Eaters were tracking her at the time, so…"
"Diana Greengrass?" Dumbledore asked calmly.
"Yes, that foolish girl." Slughorn nodded. "The Dark Lord had already taken notice of her. He was too weak to openly target a Ministry official, so he had her followed instead… and in the process, my location was exposed."
"I see."
"You know Tom and I were close," Slughorn went on. "I understand him well. Surely you can imagine the position I was in, Albus. I had no choice. I'm not brave enough to face death directly. Though in my heart, I always wished to stand on your side."
"I can understand that," Dumbledore said evenly. "Otherwise, you would not have hidden yourself after Tom's return. But you betrayed your student so easily?"
"You mean Diana?" Slughorn shrugged. "Yes, I suppose I did. But the Dark Lord had already set his sights on her. All I did was inform him that she was attempting to create a Horcrux for her daughter—and the Dark Lord happens to be quite the expert in that particular field. He had his people find her. Between threats and temptation, the foolish girl fell into his trap."
Dumbledore frowned but remained silent.
"The Dark Lord's true target was your student, Jon Hart, wasn't it?" Slughorn continued. "I don't know the exact details. Fortunately, he proved rather smarter than Diana. Or perhaps she finally came to her senses at the last moment. In any case, the Dark Lord's scheme failed that time, didn't it?"
He paused briefly before adding,
"I rather like that boy myself… even if he did pry my greatest secret from me."
"The moment I boarded the Hogwarts Express and escaped the Dark Lord's immediate control, I did everything I could to warn him. Diana's daughter—that absent-minded girl, that lovestruck child whose thoughts are written all over her face—I knew she had a way to contact Hart. So I quietly told her the truth."
Noticing Snape's cool gaze from the corner of his eye, Slughorn cleared his throat and lowered his voice.
"Of course, I won't deny that I revealed everything I knew about Hart to the Dark Lord. But that was purely for self-preservation—a temporary measure! Besides," he added hurriedly, "the boy is perfectly fine to this day, isn't he? Surely I deserve at least a little credit for that?"