Harry told his friends about his adventures in Charms class the next morning. Draco was disappointed that Harry had finally succeeded in getting the memory using 'Gryffindor' tactics, but declared that he didn't really expect any better. Ron was excited by the idea of Harry going along to destroy the next Horcrux, and asked repeatedly if he could come too.

"What did Dumbledore say about the cup?" Hermione asked as Professor Flitwick passed them.

"He thinks it's another Horcrux, but there's no way to get to it without permission from someone in the family."

Draco snorted. "Well, since 'family's' not likely to include me, the chances of that happening are less than zero."

Harry agreed. "Dumbledore will find a way though."

"So that's four horcruxes, right?" Ron asked. "The diary, the ring, whatever Dumbledore is tracking down, and the cup. How many more are there?"

"Probably two. The snake, and who knows what else."

Ron ducked as a stray cloud flew towards his head. "What's up with Dean today?" he gestured in the direction the cloud had come from.

"Ginny broke up with him last night," Hermione said. "They've been pretty rocky for a while but it's over for real now."

Harry felt his heart soar strangely at this information. Before he knew it an argument had started in his head. Maybe if he talked to Ron first…

Finally the class ended. Harry and Draco dashed off to an empty bathroom, eager to try the spell they had found in Harry's Potions book.

"You said 'sectum' means cut," Harry said as he examined the page again. "It does say For Enemies. Are you sure you don't want to try it on me instead?"

"Think I'm scared, Potter?" Draco said tauntingly. "Don't worry. I'll be fine."

Harry raised his wand and pointed it at Draco. "Let's see if this is as good as Levicorpus. Sectumsempra!"

The smile fell from Harry's face immediately. Draco collapsed to the floor, his hands scrabbling at the deep cuts that had appeared across his face and chest. He gasped in pain as blood pooled beneath him.

Harry fell to his knees, not realising that he was screaming. The bathroom door burst open and a figure in dark robes rushed in.

Professor Snape passed his wand quickly over Draco while he muttered a spell that sounded like a song. Harry watched, horrified, as the cuts began to close. After Snape had repeated the spell for a third time he barked out an order.

"Help me get him to the infirmary. If he takes Dittany right away we might avoid scarring."

Harry hoisted Draco up onto his shoulder and stumbled out of the bathroom. Together he and Professor Snape carried the boy to the infirmary, where Madam Pince took charge and led him to a bed.

Snape rounded on Harry. "What were you doing?" he demanded.

"We were just testing a spell. We found it in a book and we were curious." Harry swallowed the lump in his throat as he heard Draco moan in pain from behind a curtain.

"Congratulations on successfully performing your first Dark Magic," Snape said drily. Harry could feel him looking into his mind and knew that he couldn't stop what was coming. Unbidden, an image of his Potions textbook swan into his mind.

"Bring me your school books," Snape growled. "All of them."

Harry rushed from the infirmary, thankful that he had left his bookbag in the bathroom. He sprinted down to retrieve it, then ran up to Gryffindor Tower.

"Ron!" Harry exclaimed as he saw his friend climbing through the portrait hole. "I need your Potions book, quick!"

"What for?" asked Ron as he rifled through his bag.

"I hurt Draco. It was an accident. Snape saw the book in my head." He snatched the book out of Ron's hands and shoved the Half-Blood Prince's book at him. "Hide this somewhere, I'll get it later." He turned and ran back to the infirmary.

"Roonil Wazlib?" Snape asked, surveying the Potions book he had found in Harry's bag.

"Yes sir, that's my nickname." Harry answered. He looked away as Snape gazed piercingly at him.

"Fifty points each from Gryffindor and Ravenclaw," Snape drawled after a moment. "For lack of forethought when using potentially dangerous spells. You and Mr. Malfoy will both be serving detention with me Friday evening at five o'clock. Be thankful I was nearby, Mr. Potter. Draco could easily have died in that bathroom."

Harry shuddered at the thought. "Thank you for saving him Professor," he muttered. "We'll be more careful in the future."

"See that you are." Professor Snape drifted out the door.

Harry waited for Madam Pomfrey to release Draco. After half an hour, a good deal of Dittany, and a blood replenishing potion, she pronounced him almost as good as new and allowed Harry to help him back to his dorm for a mandatory nap.

"Detention?" Draco groaned. "And fifty points? The Ravenclaws are going to kill me."

"We're lucky," Harry said. "Snape knew what the spell was. He said you could have died."

Draco cocked his head. "You said he looked at your potions book straight away? I wonder…"

"I don't think it means much. I'm awful at Occlumency. It was the first thing he saw in my head."

"Still," Draco said as Harry lowered him onto his bed. "It could mean something. I'll have to check."

"It doesn't matter anyway," Harry said. "I'm going to get rid of the book. Hide it somewhere. I can't risk taking it to class and Snape finding it."