Harry prodded Bellatrix with his foot as Kreacher pressed a pad of folded-over linen bandage against Harry's right forearm. Harry had cleaned the blood away, but he didn't know any healing spells. Bellatrix made a small noise, and shifted against the floor. She was alive. Harry sighed, then winced as Kreacher wrapped the tail of the bandage around Harry's arm to hold the pad down.

"Thanks, Kreacher," Harry said absently, then remembered who he was talking to. "Tidy the kitchen and make me another sandwich," he said sharply. Kreacher scurried back to the bench, and Harry frowned down at Bellatrix. Information, he reminded himself. She was useful, and Dumbledore would see her punished when she stopped being useful. But for now…Harry sighed again, and shook his head. "Kreacher," he said, not looking away from Bellatrix. "Do you know anything about the library here?"

*

"A Warlock's Primer Upon Anatomie," Harry read from the spine of the book Kreacher had brought him. "This looks like it was written in the twelfth century." He opened the book, and scanned the cramped, blocky handwriting at the top of the title page. "Sorry, fifteenth. This really has healing charms in it?" He flicked forward a few pages, and stopped to stare at a carefully drawn diagram of a man being ripped in half on a rack. "Bloody hell."

"Master Regulus learnt many things from this book," Kreacher said, twisting his long, crooked fingers together. "Oh yes, many things."

"Right," Harry said, leafing through the book again. "Is there an index, or…ah. The passages and motions of blood. Curses, hexes…how do I stop it flowing…" He leaned in close to the page; the author's cramped cursive was almost unreadable in places. Harry glanced at Bellatrix again, and walked away to the kitchen table. He put the book down, and used his left hand to hold his wand against the cut on his forearm. "Tela." Harry felt an odd stretching sensation in his forearm, and removed the pad to see that the cut had clotted and looked well on its way to being healed. "Just like magic," Harry said to himself. He tapped the cut again, and added the anti-infection spell from the book. "Cruosignus."

He glanced at Bellatrix, still crumpled against the wall in the corridor. She'd hit her head pretty hard; she probably had a concussion, maybe even brain damage. Harry smiled slightly, then shook his head. Dumbledore. The war. Information. The book seemed to be organised by systems of the body, and Harry flipped past the circulatory and lymphatic to get to the nervous system. There was a diagram of a brain, several pages about the 'many and varied energies of the mind', and then a section about actual magic. Harry picked out a diagnosis charm, and cast it at Bellatrix. Her head glowed blue with a trace of green – nothing but a sore head. Wonderful. He took a sandwich on a plate from Kreacher, put it on top of the closed book, and carried both of them upstairs to his room, stepping over Bellatrix on the way.

*

The next morning, Harry went down to the kitchen to get breakfast. Bellatrix was sitting at the table, eating an omelette. Kreacher lurked in the corner.

"How's your head, Lestrange?" Harry said as he sat down opposite her. She narrowed her eyes, and her hand twitched towards her pocket. Harry knew that she wanted to curse him, and that she knew it was pointless trying. He smiled brightly, then looked at Kreacher. "Kreacher. A glass of orange juice, two fried eggs, and some bacon, please." Kreacher made Harry breakfast in a sullen silence, and hovered the plate over to land with a loud thunk. Harry picked up his fork, and noticed Kreacher watching him. Harry frowned. "Kreacher, did you poison this?"

"No," Kreacher muttered, and after a pause added "Master." Harry stared at the house-elf in surprise; Kreacher stared at his feet, and disappeared with a pop. Disconcerted, Harry returned his attention to his breakfast and caught Bellatrix looking at him again.

Harry knew what murderous rage looked like – he had seen it, and felt it. Bellatrix didn't look like she wanted to kill him. In fact, it was something like the way Snape looked at one of Harry's potions, and sometimes Harry himself: both calculating and disappointed, as if Harry was an essay covered in red-inked corrections.

"What?" he said reflexively.

"I'm trying to understand why you were prophesied to defeat the Dark Lord," Bellatrix said. "I mean, look at you."

Harry ate a forkful of bacon, and tried not to feel insulted. A small part of him whispered that Bellatrix was right, that he didn't have a chance against Voldemort. He pushed that voice away. "The prophecy didn't choose me," he said, thinking out loud. "Voldemort did."

"The Dark Lord!" Bellatrix said fiercely.

"What do you care what I call him?" Harry said, matching her tone. "He's not your Lord any more."

Bellatrix waved a hand. "Call him what you like. Your idiocy is no concern of mine." There was silence for a little while, Harry working through his breakfast as Bellatrix stared at the table. Then Bellatrix spoke again. "What do you mean, he chose you?"

The prophecy, he had hinted at part of the prophecy. Harry opened his mouth to change the subject, distract Bellatrix by bringing up her husband again – and stopped himself. Bellatrix was imprisoned by the Unbreakable Vow, literally incapable of disobeying Dumbledore. She was probably the only person not actually in the Order that Harry knew wouldn't tell anyone else.

"He chose me," Harry said. "That's what was in the rest of the prophecy. It said he would 'mark me as his equal', and he did. It was me or Neville, and he chose me."

"Longbottom," Bellatrix murmured. She smiled, as if she was remembering a particularly good joke. "Or Potter. The incompetent or the half-blood." She looked Harry in the eyes. "That was all? That was the prophecy he has spent a year seeking?"

"That's it," Harry lied, not meeting her eyes but not looking away.

"Then why would the old fool…round-the-clock guards for a scrap of prophecy already fulfilled!" Bellatrix frowned at the table. "No. Dumbledore might move in circles, but never aimlessly. Ah. It draws us into the open," she looked at Harry, "forces the Dark Lord to reveal his return, negates all that wonderful publicity you were getting, Potter. Dumbledore is transformed from senile old Headmaster to the de facto leader of the nation; and you, Potter, you become a misunderstood hero rather than a pathetic glory hound." Her eyes gleamed with amusement, and Harry was again reminded of Sirius, strong and proud and wild.

Harry's throat felt strange. He swallowed to get rid of the sensation. "I'll be sure to write Voldemort a thank-you note."

Bellatrix twitched, but did not correct him. "Prophecy! What a useless thing." She drew her wand, and Harry went for his, but she merely raised an eyebrow and hovered her plate over to the kitchen bench. "Who taught you to duel, Potter?"

"Voldemort, mostly," he said, and sure enough she twitched again. He held back a smile.

"Whoever it is," she went on, "they're useless, based on your performance last night. Or you are an exceptionally dull student. Perhaps both."

"And which of us spent the night unconscious on the floor?" Harry said, this time not holding the smile.

"I am geas-bound not to attack you, Potter," Bellatrix said. "You," she pointed her wand at him for emphasis, "have no such restriction, and had Dumbledore not had the foresight," she spat the word, "to include physical harm in his prohibition, I would have killed you three times over yesterday."

Harry would have disagreed, but it was true. "So?" he said.

"So, according to prophecy, you are the only one who can defeat the Dark Lord, and at present you would have difficulty defeating a grilled haddock in a duel." Bellatrix shifted in her seat. "As long as…he…remains a power, I must cling to Dumbledore for survival. As you pointed out last night," she added bitterly.

"How terrible for you," Harry said.

"Indeed," Bellatrix said, and smiled – or rather, bared her teeth. "So I will have to teach you."

Harry blinked. "What?"

"I don't intend to moulder away here, waiting for Dumbledore to decide I'm no longer of use. If I want a future, I need the Dark Lord dead. Unfortunately, I'm not the subject of the prophecy – you are."

"I – you –" Harry took a deep breath. "I don't want anything from you." He took a deep breath. "You're an evil, murdering bitch who wants to kill all my friends."

"But it's nothing personal, Potter," Bellatrix said, pouting. Harry glared at her, and she laughed in his face, for a moment sounding as carefree as a child. "Really, Potter," she said, "you're not going to kill the Dark Lord with stunners and schoolboy jinxes."

"And I suppose you'd love to teach me some Dark magic," Harry said.

Bellatrix smiled. "I could teach you many things."

"Out of honest selflessness, I suppose."

"Merlin's teeth, Potter, try for a little wit. Push through that Gryffindor bravado and think. I need the Dark Lord dead, and I am unable to kill him; you want him dead, yet your skill is vastly inadequate to the task."

"Oh, yes," Harry said brightly. "A few days of lessons from the ex-Death Eater, and I'll be ready to kill Voldemort in an open duel, I'm sure."

"He would tear you to shreds," Bellatrix said. "But, with some training, the element of surprise…if he's ill…or concussed…you may have a small chance." She shrugged carelessly. "If nothing else, it will give me a source of amusement."

Harry sat back in his chair. "You're serious."

"Deadly serious, even," Bellatrix said, running one long finger up and down her wand. Harry stood up and walked out of the kitchen, leaving his breakfast half-eaten. "Think about it!" Bellatrix called after him. He didn't have to. Harry had been humiliated so many times – in the graveyard with Voldemort, in the Ministry with the Death Eaters. He had been helpless so many times, scraping by on luck and quick reflexes. Much as he hated the idea of learning from Bellatrix, he already knew what his answer was going to be.

*

"Now, class," Bellatrix said sternly from the front of the empty storage room. "Pay attention. There will be a practical exam later on."

Harry folded his arms. "If this is just going to be you laughing at me…"

"Very well." Bellatrix twirled her wand between two fingers. "What do you already know? Malfoy said something about you running a little defence club at school." Harry hesitated. "Oh, come on Potter, I'm on your side now."

Harry glared at her. "No, you're not."

"No, I'm not," she agreed, and waited.

"Just the basics," Harry said. "Disarming, stunning, blasting hex, exploding curse, basic shields, the Patronus charm."

"Oh, I've underestimated you. A haddock would be in serious danger, should it face you on the battlefield."

Harry ground his teeth. If she didn't start actually teaching him, he would just walk away. But before he did…"I'm sorry to disappoint you, Professor Lestrange."

"Black!" Bellatrix snarled, her stern expression vanishing as she dropped into a dueling stance. "The name is Black."

"Sirius's name was Black," Harry said. "You don't get to take his name!"

"He gave up the right to that name when he betrayed us."

"And you gave up yours when you killed him!" Harry shouted. He realised he had raised his wand, and lowered it. He'd had enough of blasting Bellatrix into walls; it wasn't making him feel any better. "You killed him for nothing. For a man who threw you away. And nothing you can say is going to make me forget that."

"He was my family too, Potter," Bellatrix said, so quiet that he almost didn't hear her.

"I can see how much that mattered to you," Harry said bitterly.

"You don't understand."

"Understand family? No, I guess I don't. I wonder why that could be." They both fell silent.

"Starting with counter-curses, then," Bellatrix said, breaking the silence. "Cancellation charms will work on most curses, but they take more time and concentration than I think you'll have in a real fight."

"You're going to teach me all the counter-curses?" Harry asked, still angry but slightly interested despite himself.

"And then I'll name all the stars in the sky. Of course not, Potter. Just the curses that we – that Death Eaters like to use." She smiled. "Mostly the painful, debilitating ones. This is the blood-boiling curse." She flicked her wand at the wall, and a tendril of dark red light shot out and left a scorch mark on the wall. "The counter-curse is Norcurvare, emphasis on the first and third syllables. The motion is a downward chop…"