Harry had said Lupin had agreed to give the entire coven Patronus Lessons, but he seemed surprised as they all filed into the empty classroom Thursday night.

"Miss Lovegood?" Lupin said, blinking.

"Hello Professor," Luna said, her voice dreamy. "Your socks look much better today."

Lupin shot Harry an odd look, and Harry shrugged defensively.

"You said I could bring the group of people I study advanced magic with," he reminded Lupin. "Well, this is that group."

Lupin cast his eye slowly over them all, lingering on Hermione and Blaise. Hermione raised her chin defiantly, folding her arms.

"Is there a problem, professor?" she asked.

Lupin paused, before shaking his head. "Not at all."

Hermione watched as Lupin put a large packing case onto the teacher's desk. They all looked at it curiously.

"What's that?" Harry asked.

"Another boggart," Lupin said, taking off his cloak. "I've been combing the castle, and I was lucky enough to find this one lurking inside Mr. Filch's filing cabinet. It's the nearest we'll get to a real dementor." He paused. "The boggart will turn into a dementor when he targets Harry, at least, so we'll be able to practice on him."

"Oh!" Hermione exclaimed. "How clever!"

Susan was looking at Harry. "Your boggart is a dementor?"

"Yeah. I mean, I think it is," Harry admitted, wincing. "I didn't get to go in class."

"Fair enough." Susan shrugged, mildly impressed. "I figured it'd be You-Know-Who."

"So…" Professor Lupin took out his wand, and the five of them followed suit. "The spell I am going to try and teach you is highly advanced magic, realize – well beyond Ordinary Wizarding Level. It is called the Patronus Charm."

"How does it work?" Harry asked, determined.

"Well, when it works correctly, it conjures up a Patronus," said Lupin, "which is kind of an anti-dementor – a guardian that acts as a shield between you and the dementor."

Hermione recalled the silvery smoke Lupin had shot at the dementor on the train. Had that been a guardian? Tom had said a Patronus took the shape of an animal.

"The Patronus is a kind of positive force, a projection of the very things that the dementor feeds upon – hope, happiness, the desire to survive – but it cannot feel despair, as real humans do, so the dementors can't hurt it." Lupin paused. "I feel I must warn you: the charm might be too advanced for you. Many qualified wizards have difficulty with it."

"Why?" Hermione asked.

Lupin shifted his eyes to hers. "Why what?"

"Why is it so difficult?" Hermione asked. "Does it require immense personal power? Is it very particular and finicky? What makes it such a challenge?"

Lupin looked thoughtful for a long moment.

"It requires great personal power, surely," he said, "but the greatest difficulty relies in the origin of the Patronus itself. The Patronus Charm requires tying an emotional state to magic, which is an advanced technique in Charms – in this case, the caster must concentrate on a single, happy memory."

"A memory?" Blaise frowned.

"Yes," Lupin said. "Focus on a single, happy memory, and try and feel the emotions you felt at that time. While holding onto those emotions, you cast the charm, fueling the Patronus into being."

Hermione wondered when she had felt the happiest. She settled on seeing her parents again and the end of her first year, trying to immerse herself in the sheer joy and happiness she had felt as they hugged her.

"The incantation is this—" Lupin cleared his throat. "Expecto patronum!"

"Expecto patronum," they all repeated.

"Good. Now – focus on your happy memory…"

Hermione focused her thoughts on her happy memory, trying to immerse herself and her magic into the emotions she had felt at that moment as she cast. "Expecto patronum – Expecto patronum—"

Something silver suddenly whooshed out of the end of Hermione's wand, startling her. A moment a later, a similar wisp of silvery gas escaped from Harry's wand a moment later.

"Did you see that?" Harry said excitedly. "Something happened!"

"Very good." Lupin was smiling. "That's what you're going for."

Hermione was frowning down at her own wand. "I thought the Patronus was supposed to be an animal?"

Lupin's lips quirked. "Been reading ahead, Miss Granger?"

Hermione flushed. "…maybe a little."

"A fully corporeal Patronus will take the form of an animal, but many wizards never get to that point," Lupin explained, smiling. "Many only manage a silvery shield. A fully corporeal Patronus requires immense personal magical power."

"Do we want to try for that?" Blaise asked. "Should we try casting one at a time?"

"It's worth a shot," Susan said, shrugging. "Want to go first, Harry?"

Lupin looked confused.

"You can all cast at the same time," he said slowly. "I don't think you'll distract each other enough—"

Hermione realized the issue in a heartbeat, turning to look at Harry, aghast.

"You never told Professor Lupin who we were?" she groaned, clapping a hand to her forehead. "What did you tell him?"

"That I had studied advanced magic with you all in the past," Harry protested, "and that you would all help defend me from dementors if it came to that!"

Hermione groaned again. Lupin looked very lost.

"Professor Lupin, we're Harry's coven," Luna said, looking up at him. "That's why Harry brought us with him – we've all bound our magic to each other's."

Lupin's jaw dropped.

"A coven?" Lupin sputtered. "You – you—a coven?"

"That's what she said, isn't it?" Blaise muttered testily, but Hermione elbowed him and gave him a sharp look.

Lupin looked pale. He was leaning back against the desk.

"What possessed you to do such a thing?" he asked finally, his eyes wide as he looked over them with a new wariness. "A coven… your parents would have never—"

"If the Potters had been in a coven, they might have been able to better protect their house," Susan shot back, her face darkening. "Don't you dare go condemning covens."

"Dumbledore is fully aware that we've coven-bonded," Hermione informed Lupin. "And covens aren't inherently Dark."

"And the bond allows us to share our power with each other," Harry said. "Which is why – if a Patronus requires immense magical power, if we go one at a time, we can take turns pulling on everyone's power to try and get a corporeal one."

Lupin looked stunned. Time stretched on as he looked at them all silently, his face inscrutable.

"I… I don't see why not," he said finally. He looked at Harry. "Are you ready to try on a dementor?"

Harry faltered.

"Err—"

Harry gripped his wand very tightly, moving to the middle of the classroom. He looked like he was concentrating very hard, but his face was pale.

"You can do it, Harry," Hermione encouraged from behind him. "You can do this."

"Just focus and pull on us, Harry," Susan urged. "We've got your back."

Lupin raised an eyebrow. "Ready?"

Taking a deep breath, Harry nodded.

Lupin grasped the lid of the packing case and pulled.

A dementor slowly rose from the box, its hooded face turned toward Harry, with one glistening, scabbed hand gripping its cloak. The lamps around the classroom flickered and went out. The dementor stepped from the box and started to sweep silently toward Harry, drawing a deep, rattling breath, and a wave of cold broke over Hermione.

"Expecto Patronum!" Harry yelled. "Expecto Patronum! Expecto—"

Harry seemed to fall in slow motion, crumpling to the ground, and Lupin hurried forward, pushing the boggart back into the box as it turned into the silvery orb of the full moon in front of him. Susan had gone to Harry, shaking him, while Luna and Blaise looked shaken, but Hermione was watching Lupin with thoughtful eyes.

On the floor, Harry had jerked back to life. He was flushing in embarrassment.

"Are you alright?" asked Lupin.

"Yeah…" Harry pulled himself to his feet with Susan's help, leaning against her.

"Here – eat this before we try again." Lupin handed him a chocolate frog. "I didn't expect you to do it your first time; in fact, I would have been astounded if you had…"

"What causes boggarts?" Hermione asked Blaise quietly. "I remember they're amortal, but what causes a boggart to manifest?"

Blaise looked at her sideways.

"I think they form from residual magic around large groups of magical people," he said, keeping his voice low. "Lupin made them sound like they just 'happened' from time to time."

Hermione considered this.

"Do you think we could find one on our own?" she asked quietly.

"Maybe." Blaise raised an eyebrow. "If we were lucky."

"Do you think we could purposefully create boggarts on our own?" Hermione asked, watching as Harry readied himself again for another try.

Blaise smirked, his eyes glinting.

"Make a boggart farm?" he said softly. His eyes gleamed. "I don't know if it's ever been done, but if we wanted to, I'm sure we could try."