“Sir, is it true that Professor Merrythought is retiring?

“Sir, is it true that Professor Merrythought is retiring?” he asked.

“Tom, Tom, if I knew I couldn't tell you,” said Slughorn, wagging a reproving, sugar-covered finger at Riddle, though ruining the effect slightly by winking. “I must

say, I'd like to know where you get your information, boy; more knowledgeable than half the staff, you are.”

Riddle smiled; the other boys laughed and cast him admiring looks.

“What with your uncanny ability to know things you shouldn't, and your careful flattery of the people who matter—thank you for the pineapple, by the way, you're quite

right, it is my favorite—”

As several of the boys tittered, something very odd happened. The whole room was suddenly filled with a thick white fog, so that Harry could see nothing but the face of

Dumbledore, who was standing beside him. Then Slughorn's voice rang out through the mist, unnaturally loudly: “—you'll go wrong, boy, mark my words.”

The fog cleared as suddenly as it had appeared and yet nobody made any allusion to it, nor did anybody look as though anything unusual had just happened. Bewildered,

Harry looked around as a small golden clock standing upon Slughorn's desk chimed eleven o'clock.

“Good gracious, is it that time already?” said Slughorn. “You'd better get going, boys, or we'll all be in trouble. Lestrange, I want your essay by tomorrow or it's

detention. Same goes for you, Avery.”

Slughorn pulled himself out of his armchair and carried his empty glass over to his desk as the boys filed out. Voldemort, however, stayed behind. Harry could tell he

had dawdled deliberately, wanting to be last in the room with Slughorn.

“Look sharp, Tom,” said Slughorn, turning around and finding him still present. “You don't want to be caught out of bed out of hours, and you a prefect...”

“Sir, I wanted to ask you something.”

“Ask away, then, m'boy, ask away....”

“Sir, I wondered what you know about... about Horcruxes?”

And it happened all over again: the dense fog filled the room so that Harry could not see Slughorn or Voldemort at all; only Dumbledore, smiling serenely beside him.

Then Slughorn's voice boomed out again, just as it had done before.

“I don't know anything about Horcruxes and I wouldn't tell you if I did! Now get out of here at once and don't let me catch you mentioning them again!”

“Well, that's that,” said Dumbledore placidly beside Harry. “Time to go.”

And Harry's feet left the floor to fall, seconds later, back onto the rug in front of Dumbledore's desk.

“That's all there is?” said Harry blankly.

Dumbledore had said that this was the most important memory of all, but he could not see what was so significant about it. Admittedly the fog, and the fact that nobody

seemed to have noticed it, was odd, but other than that nothing seemed to have happened except that Voldemort had asked a question and failed to get an answer.

“As you might have noticed,” said Dumbledore, reseating himself behind his desk, “that memory has been tampered with.”