Snape returned ten minutes later. He stepped into the bathroom and closed the door behind him.
“Go,” he said to Myrtle, and she swooped back into her toilet at once, leaving a ringing silence behind her.
“I didn’t mean it to happen,” said Harry at once. His voice echoed in the cold, watery space. “I didn’t know what that spell did.”
But Snape ignored this. “Apparently I underestimated you, Potter,” he said quietly. “Who would have thought you knew such Dark Magic? Who taught you that spell?”
“I—read about it somewhere.”
“Where?”
“It was—a library book,” Harry invented wildly. “I can’t remember what it was call—”
“Liar,” said Snape. Harry’s throat went dry. He knew what Snape was going to do and he had never been able to prevent it…
The bathroom seemed to shimmer before his eyes; he struggled to block out all thought, but try as he might, the Half-Blood Prince’s copy of Advanced Potion-Making swam hazily to the forefront of his mind.
And then he was staring at Snape again, in the midst of this wrecked, soaked bathroom. He stared into Snape’s black eyes, hoping against hope that Snape had not seen what he feared, but—
“Bring me your schoolbag,” said Snape softly, “and all of your schoolbooks. All of them. Bring them to me here. Now!”
There was no point arguing. Harry turned at once and splashed out of the bathroom. Once in the corridor, he broke into a run toward Gryffindor Tower. Most people were walking the other way; they gaped at him, drenched in water and blood, but he answered none of the questions fired at him as he ran past.
He felt stunned; it was as though a beloved pet had turned suddenly savage; what had the Prince been thinking to copy such a spell into his book? And what would happen when Snape saw it? Would he tell Slughorn—Harry’s stomach churned—how Harry had been achieving such good results in Potions all year? Would he confiscate or destroy the book that had taught Harry so much… the book that had become a kind of guide and friend? Harry could not let it happen… He could not…
“Where’ve you—? Why are you soaking—? Is that blood?”
Ron was standing at the top of the stairs, looking bewildered at, the sight of Harry.
“I need your book,” Harry panted. “Your Potions book. Quick… give it to me…”
“But what about the Half-Blood—”
“I’ll explain later!”
Ron pulled his copy of Advanced Potion-Making out of his bag and handed it over; Harry sprinted off past him and back to the common room. Here, he seized his schoolbag, ignoring the amazed looks of several people who had already finished their dinner, threw himself back out of the portrait hole, and hurtled off along the seventh-floor corridor.