By the time spring leaned into summer, the Duelling Club floor glowed most evenings. Moonspit had been the beginning. That variant was meant to teach them the shape first. No happy memory crutch yet. They had to see it before they could cast it.
After they'd stopped producing drifting mist and accidental fireworks, Cassian added two more.
Luna named them of course. "If Moonspit is the mind, and if the others are the spine and the pulse..."
He'd blinked at her. "Go on."
"The spine holds you upright," she said. "Even when you're frightened. And the pulse keeps you here. Even when something tries to pull you out."
Spineguard and Heartflare.
Moonspit - mental construct.
Spineguard - will.
Heartflare - emotional ignition.
Three parts of one spell. Mind. Will. Feeling.
By late May, the older lot could switch between them without collapsing into silver fog. The younger ones were still at war with themselves.
Cassian clapped, shaking the rafters with the force of it. "Right. Split up. First-years on the left. Third-years centre. Fifth and up, you're refining."
Aye ayes rolled across the hall. He walked straight to the youngest circle.
James stood stiff as a fencepost, wand held too tight. Alys hovered beside him, already half-lit with nerves. Fawley stared at the practice dummy hard.
"First-years," Cassian said, hands behind his back. "You're not touching Heartflare yet. You'll burn yourselves out. We're doing Moonspit and a light Spineguard."
Alys raised her hand. "What's light Spineguard?"
"It's you standing your ground without crying," he said. "Start with Moonspit."
He walked to James. "Picture it. The outline. Weight. How it stands."
James swallowed. Closed his eyes.
The air shimmered faintly. A wobbling silver flickered out, head too large for its body, legs melting into mist.
Fawley stepped forward. His Moonspit came out better. A narrow, fox-like shape, though it kept blinking out at the tail.
"Better," Cassian said. "You're seeing it. Now hold it."
The shape steadied for three heartbeats before dissolving.
Alys' turn. Her silver mist barely formed a spine before it collapsed.
She stared at the floor.
Cassian crouched to her height. "What'd you see?"
"A cat," she muttered.
"What kind?"
She hesitated. "Just... a cat."
He nodded. "That's your problem. Magic hates 'just'. Tabby? Big? One-eyed pirate menace?"
Her mouth twitched. "Small. Black. White paws."
"Good. Try again. Give it bones."
She lifted her wand.
This time they came neat. A small feline outline, tail curling before fading.
James leaned closer. "That was good."
Cassian stood. "That's Moonspit. You build it with your head. Don't rush it. If you can't see it, it won't stand."
He straightened and moved to the third-years.
Dennis Creevey was already mid-cast, silver sparks spitting from his wand. Nigel Wolpert stood beside him, muttering under his breath like he was revising for Charms.
"Spineguard," Cassian said. "Show me."
Dennis took a deep breaht and thrust his wand forward. "Expecto-"
"Drop the words," Cassian cut in. "Spineguard doesn't need a shout."
Dennis tried again. This time the silver light came hot and dense with a thick band of glow that settled around him like a curved shield.
Cassian nodded. "There it is. That's will."
Nigel stepped in next. His light flared bright, then fractured.
"You're thinking about it too hard," Cassian said. "Spineguard's simple. Plant your feet. Do."
Jimmy Peakes managed a stronger band, though it trembled. Natalie McDonald's version came softer but wider, covering more ground.
"Good," Cassian said. "You lot understand the difference now? Shape first. Then resistance."
He left them to practise and crossed toward the fifth-years.
Ginny Weasley already had a full-bodied Patronus trotting in a circle around her. A shimmering, full fledged horse.
She grinned and let the horse dissolve. Switching to Heartflare. This time the silver burst came explosive and bright in a surge that rippled outwards in a wave.
Colin Creevey blinked. "Blimey."
Cassian nodded. "That's Heartflare. You're fuelling. Pure emotion. Quick, violent and controlled."
Luna stood beside her. Her Heartflare bloomed, a lot less violent.
Ron's Heartflare exploded too wide, nearly knocking Seamus back a step.
"Tone it down," Cassian called. "You're not duelling a thunderstorm."
Ron scowled and tried again.
The silver burst shot out of his wand, then collapsed in on itself like a firework dunked in water.
Cassian let out a breath.
"Right. That's enough flailing."
He raised his voice. "Fifth- and sixth-years who still can't cast a full Patronus, over here. If you've got a corporeal one, go help the younger lot."
Ginny crossed toward the third-years. Luna drifted after her, already watching Dennis' stance. Most of the seventh-years peeled away. A good chunk of the sixth followed, splitting off to guide first- and second-years through Moonspit shapes.
What remained were the stubborn ones. Fifth-years with smoke instead of substance. A handful of sixth-years who could flare but not hold. A few who'd managed Heartflare, Spineguard and Moonspit cleanly but froze when it came time to fuse them.
Cassian looked them over.
"Good," he said. "Now we stop pretending these are separate tricks."
He stepped into the centre circle and drew three quick marks in the air with his wand. One at his head height. One at his chest. One at his feet.
"Mind. Heart. Spine."
He tapped each mark as he spoke.
"You've learned the pieces. Shape. Resistance. Ignition."
He looked up at them.
"It's time to stack them."
He pointed at the three marks again.
"Start with Moonspit. Build the animal. Don't cast it. Just hold the outline in your head."
A few closed their eyes.
"Now Spineguard. Plant your feet. Feel your intent. You're standing in the memory. Don't chase it."
Shoes scraped stone as they adjusted their stance.
"Then Heartflare. Pick the moment."
Silver mist began to gather in uneven patches across the circle. Lavender's outline flickered into a hare, then thinned. Harper's smoke rose too fast and tore sideways.
"Don't rush it," Cassian said. "You're not summoning."
Neville stepped forward into the struggling group. "Think of it like stacking stones," he said to one of the Hufflepuffs. "If the bottom's crooked, the top falls."
Cassian gave a nod.
"Alright," he called. "On my count. Build it in order."
He lifted his wand.
"Three."
Lavender's hare. A badger from the Hufflepuff girl. Something bird-like from the Ravenclaw boy.
Cassian sighed.
"Closer."
Lavender looked frustrated. "It's there. I can feel it."
"Good," he said. "That means you're about to catch it."
She made a face but nodded.
He pointed at his chest.
"Balance it."
Ron looked like he was trying to hold three thoughts at once and resented all of them.
Cassian glanced toward the younger students at the far end of the hall.
"Right," he added. "Water break. Then we do it again."
***
He felt that familiar feeling the moment a few of them managed a full corporeal Patronus in the same evening. It had been gathering for months. Patronus was a high-tier spell. Ancient variants for higher-tier spells required more teaching. To make things worse, Patronus wasn't neglected by the school at all. Defence professors drilled it. Charm teachers picked it apart. Wasn't much for Cassian to add.
He dismissed the club early and rushed to his room. Which, from the outside, looked like he was running to the loo. Bathsheda understood what was coming as soon as he entered. She dropped the stack of parchment in her hand.
"Now?" she asked.
He nodded. She guided him to the couch, sat first, then pulled him down so his head rested in her lap. Her fingers slid into his hair.
He closed his eyes and the memory broke open.
Red earth beneath bare feet. Cracked ground breathing dust. He saw from within a circle of bodies. Painted skin. White ash traced across chests and arms in lines that followed muscle and bone. People stood shoulder to shoulder. Elders at the centre. Younger ones ringing them. Children kept behind a low ridge of stone.
A sickness crawled along the ground. It clung, pressing into cracks in the soil. Wherever it passed, insects curled. Leaves blackened. A woman stepped forward from the circle. Hair bound back.
She stamped her foot. Another answered. Then another. Feet striking earth in rhythm. Slow at first. Then faster. A pulse building through the ground itself. Their hands rose, palms outward. The sickness recoiled. The rhythm grew. A shape formed above them. A figure of light. Human, but larger. Outline blurred. Weapon of pale fire in hand.
The ground responded. Dust lifted in spirals around its ankles. The pulse of it travelled outward from the circle in a widening ring. The sickness writhed. From its centre, something rose. Limbs bending in ways joints shouldn't. A head too long. Eyes like hollows burned into bark.
It screeched, almost ejecting Cassian from the memory. The air buckled. One of the elders stepped forward. He struck his chest with a fist and shouted a word Cassian didn't recognise but still understood. "Begone."
The figure of light above them was clearer now. It moved with their rhythm. The weapon drove downward and as the light struck, the sickness split, peeling back, burning the earth beneath, scorching the soil. The creature lunged at the circle. Its form stretched, reaching for the children at the ridge. One of the younger men broke rank. The elder caught his wrist mid-step. Held him there. Shook his head.
The figure of light shifted position, forming a wall between the circle and the lunging shadow. Then the word came again. This time all of them spoke it.
"Expurga."
Light poured down. It burned what clung to the earth. The sickness shrank, curling inward. The creature twisted, limbs folding in on themselves as if crushed by unseen hands. The creature made one last lunge, then split apart into ash that never reached the ground. The figure of light stood a moment longer, then dissolved into the bodies below them.
The people stopped stamping. One of the elders bent and pressed his palm to the blackened earth, nodding.
The sun dipped. The circle broke.
Cassian's eyes opened slowly. Bathsheda's hand was still in his hair. He stared at the ceiling.
"What was it?" Bathsheda asked.
Cassian stared at the ceiling a moment longer, then scrubbed a hand over his face. "Wasn't a Patronus variant. Which makes sense. We already confirmed they didn't use Patronuses back then."
She nodded. A few summers back in Australia, when they'd worked with the Flamels to seal the Night Crawlers, they'd learned the Ngaralu and Magicks of that time didn't have the light spell.
"It was a purging spell," he went on. "Took a circle. Ritual of sorts. They stamped the earth, built rhythm through the ground. Then they pulled something up. White flame shaped like a person."
He pushed himself up slightly, resting on his elbows so he could see her.
"They were inviting something through themselves. Fighting spirit, I think. Ancestral maybe. Hard to tell. But it burned the corruption clean."
Her fingers stilled in his hair. "Strong?"
"Strong," he said. "The thing they were fighting didn't stand a chance."
He frowned as he remembered the spell.
"But the ground scorched with it. It was a purge. Fire through flesh and soil alike."
She tilted her head. "Could you use it on the Horcrux? On Potter?"
Cassian shook his head.
"No. It'd cook him." He sighed. "That spell doesn't discriminate between host and parasite. It burns what's there. The creature, the sickness, the earth under it. Potter wouldn't survive the first breath of it."
She hummed, eyes darting as it usually did when she thought.
"If that much force ran through a human body, it'd reduce him to cinders before it even touched that fragment of soul." He added.
Bathsheda nodded, then leaned back into the cushions.
She knew he was disappointed. He hadn't been teaching Patronus variants for academic curiosity, although he wanted all students to manage it, he admitted he was pushing them. He'd broken it down into components on purpose, forcing a spell that was heavy for half of the school. He was chasing an ancient spell. A variant that could destroy a Horcrux. Strong enough to cut the parasite out without harming the host.
She knew what he'd hoped for. And she knew it hadn't come.
"Can we change it?" She asked, holding his hand.
He looked back at her.
"The purging spell," she clarified. "Strip it down. Learn the bones. Remove the fire. Keep the intent."
He considered that.
"It wasn't built for delicate extraction," he said. "It was built for all out war."
"Spells evolve," she replied. "You've proved that often enough. If it channels collective will into manifestation, then the destructive element might not be the core. The core might be the summoning."
He nodded slowly.
"If we isolate conduit from expression," she continued, "we might redirect what answers."
"Less flame," he muttered. "More filtration."
"Yes."
He leaned forward.
"It'd need containment," he said. "Not a wide surge. A narrow channel. Focused around a single target."
"And layered," she added. "Host protected first. Wards woven into the body. Then the purge applied only to what doesn't belong."
He grimaced. "That assumes the spell can distinguish."
"It distinguished the sickness from the people in the circle."
"It still burned the land," he countered.
"Because the land was touched by it," she said. "If the corruption's anchored in Potter's soul, the spell might interpret all of him as contaminated."
He dragged a hand through his hair. "Which brings us back to the same problem. It sees presence, not ownership."
She watched him think.
"What if," she said slowly, "we borrow from Homenum."
He glanced up.
"Definition," she continued. "Before the purge, define the target. Not 'evil.' Not 'dark.' Something more specific."
He blinked, then again.
He lunged forward and caught her round the waist, nearly knocking them both back into the cushions.
"All these years I've been banging on about intent," he said against her mouth, laughing, "and I've managed to trip over my own definition. Of course."
She laughed into the kiss, fingers catching in his collar. "Took you long enough."
---
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