A few days later, Harry, Ron, and Ginny stood in line by the kitchen fireplace at the Burrow, preparing to return to Hogwarts.
Officials from the Ministry of Magic's Department of Magical Transportation had set up a temporary, one-way Floo Network connection in the Burrow's kitchen so students could return to school quickly and safely.
Harry stepped into the emerald-green flames and shouted, "Hogwarts!"
He spun at high speed, catching blurred glimpses of wizarding rooms that flashed past before he could make them out. Then the spinning slowed, and he tumbled out in a highly undignified heap in Professor McGonagall's fireplace.
As he scrambled to his feet, the Deputy Headmistress barely looked up from her work.
"Good evening, Potter. Try not to track too much soot onto the carpet."
"I swear I didn't, Professor," Harry said quickly, straightening his glasses and smoothing down his hair.
He was just about to leave Professor McGonagall's office when he stopped abruptly, as if compelled.
"Professor… may I ask… has Professor Slughorn recovered yet?"
Professor Minerva McGonagall set down her quill, adjusted her spectacles, and gave Harry a measured look. After a moment, she replied evenly, "No. Horace is still recuperating at St. Mungo's. Is there anything else?"
"No—well—yes. I mean… who will be covering Professor Slughorn's Potions classes? It won't be Professor Snape… will it?" Harry asked, stumbling over his words.
"I'm afraid I don't know, Potter. Professor Dumbledore merely informed me that he has a suitable candidate in mind," McGonagall answered calmly. "However, given Professor Snape's familiarity with the subject, it would not surprise me."
"Right… Thank you, Professor."
Ron and Ginny emerged from the fireplace moments later. Harry hastily brushed the soot from his robes and left the office with them.
...
The three of them headed toward Gryffindor Tower. Harry glanced out of a corridor window. The sun had already sunk below the horizon, and the snow blanketing the grounds lay even deeper than it had at the Burrow. In the distance, Hagrid could be seen outside his hut, feeding several Thestrals.
"What were you asking Professor McGonagall about?" Ron whispered.
"Who's covering Potions," Harry replied honestly. "She doesn't know, but she said Snape's quite likely."
"Well… we'll find out tomorrow afternoon anyway. First Potions class of the term," Ron sighed.
Harry felt his chest tighten.
If it was Snape… if it really was Snape…
He'd know those potions weren't entirely my own work. He might even uncover the Half-Blood Prince's secret.
After turning the thought over and over in his mind, and just as they were about to reach the Fat Lady's portrait, Harry suddenly spun around and bolted.
"Harry! Where are you going?" Ron and Ginny called after him.
"I'm going to the Room of Requirement. I'll be back in a minute!"
He had made up his mind. No matter what, he couldn't let Snape discover the Prince's secret. He would rather hide the Prince's copy of Advanced Potion-Making in advance.
...
He sprinted along the eighth-floor corridor.
On the way, he even knocked over a strangely dressed younger girl, barely managing to mutter an apology as he rushed past.
A few minutes later, he skidded to a halt in front of the tapestry of dancing trolls, closed his eyes, and began pacing back and forth.
I need a place to hide something… I need a place to hide something… I need a place to hide something…
He walked past the blank stretch of wall three times. When he opened his eyes, a door had appeared.
Harry yanked it open, dashed inside, and slammed it shut behind him.
He found himself standing in a room as vast as a cathedral.
It was filled with thousands upon thousands of objects: books—surely banned, defaced, or stolen; Winged Catapults and Fanged Frisbees, some still circling lazily over heaps of forbidden items; cracked bottles containing long-congealed potions; hats, jewels, cloaks, and what looked like dragon eggshells; corked bottles emitting an ominous glow; even a few rusted swords and a bloodstained battle-axe.
Harry hurried down a narrow "lane" between the towering piles, turned right past a stuffed troll, ran a short distance, then turned left beside a broken Vanishing Cabinet—the very one Christopher Patrick had disappeared into last year.
At last, he stopped in front of a large cabinet whose surface was blistered, as though it had been splashed with strong acid.
He opened it, pulled the Half-Blood Prince's copy of Advanced Potion-Making from his bag, shoved it inside, and shut the doors firmly.
Just as he was about to leave, he noticed something else lying on the floor.
It was a thin book with a slightly yellowed cover.
"Wait… how did this end up in my bag?" Harry muttered, startled. His thoughts drifted back to a few days earlier.
That day in the Burrow's basement, when he had opened the gift addressed to Professor Gideon Prewett, he had been surprised to find a book inside—
A 1978 edition of The Wonderful Quidditch Balls.
As a devoted Quidditch enthusiast—and with little else to do in the gloomy basement—Harry had read through it several times while lying on his bed.
Much like the Prince's Advanced Potion-Making, this book was densely covered with handwritten notes. It was obvious that its former owner had been an exceptional Seeker. Some of the insights about Quidditch were so sharp that even Harry found them eye-opening.
He had thought he'd left the book at the Burrow. Somehow, he must have slipped it into his bag without realizing it.
"Should I… leave this here too?" Harry murmured.
He reopened the blistered cabinet and placed The Wonderful Quidditch Balls on top of Advanced Potion-Making.
For a split second, the book in his hands felt strangely hot.
Harry immediately changed his mind.
He pulled The Wonderful Quidditch Balls back out and returned it to his bag.
I can still read it when I've got time, he thought.
...
He stepped back out of the narrow aisle.
As he passed the broken Vanishing Cabinet, a pale face suddenly appeared directly in front of him, as though someone had been standing there all along.
Harry Potter nearly jumped out of his skin.
The other boy looked just as startled.
"Potter?"
"Malfoy?"
Both of them instinctively raised their wands.