Cassian led them down the familiar narrow stairway when he felt a pair of eyes watching from the shadows.
He didn't hesitate. His wand snapped toward the shadows without so much as a warning word.
Light burst out, thin tendrils that split and twisted, stretching. They slithered forward fast, crawling across the stone walls. The shadows peeled back. A low shape hunched near the corner, canine frame crouched low, eyes catching the light, yellow, wild, panicked.
Cassian's spell caught its hind leg. The thing jerked, claws scraping stone as it tried to pull away, but the tendrils tightened.
Harry froze behind him. Neville looked ready to run.
"Stay put," Cassian snapped, shielding them as he pulled them behind him.
The creature snarled, a dry, broken sound, and lunged forward, but the spell dragged it back. Its paws scrabbled at the floor. Then the head tilted.
"What, what is it?" Harry whispered.
Neville froze, "I-it's the grim."
The thing twisted again, then hissed as the tendrils flared and snapped tighter. Its hind leg bulged unnaturally, and for half a second, Cassian caught a flash of fabric with stripes.
Then it snapped back into the hock of a dog.
The tendril, stretched by the sudden shift, slipped off clean.
"Shit," Cassian hissed.
The creature bolted, claws scraping the floor, and vanished into the dark.
"Lumos!" Cassian flicked his wand sharply.
His wand flared, blasting the corridor in a solid shaft of white so bright it split through the dark like someone'd taken a lightning bolt and jammed it in a torch.
Harry and Neville both flinched, turned away with their arms thrown up, faces twisted as the light burned across the stones.
The dog yelped again, shooting left, deeper into the castle.
"Bloody..." Cassian muttered, flicked his wrist. Dozens of pinpricks of light shot from the tip of his fingers, scattering in every direction, clinging to walls, corners, the low arches ahead.
"Stay close," he said, grabbing both boys by the back of their collars and yanking them forward.
They didn't argue.
"Where did it go?" Neville whispered, voice small.
Cassian took a breath. "No idea."
Footsteps reverberated from corridors all around. McGonagall came in first, wand drawn, Lupin on her heel. Sprout not far behind, then Bathsheda and Flitwick. Snape, of course, slid in like a bat escaping sunlight.
"What happened?" McGonagall asked, eyes scanning the corridor, landing on the boys, then the walls, then Cassian.
Neville blurted, "It was the Grim!"
The professors stilled.
Snape made a noise somewhere between a sigh and a sneer. "What are you babbling about, foolish boy."
"It was an all-black dog, Severus," Cassian cut in. "Grim as your face."
That shut him up.
McGonagall's frown deepened. "A Grim?"
"Bigger than any dog I've seen," Cassian said. "Caught part of its leg. It shifted. Not a full Transfiguration, more like... partial."
Flitwick had already started inspecting the scuffed floor where the creature had scrambled free. "Anything you noticed?"
"Clothes," Cassian said. "Just for a second. Looked like prison stripes."
Flitwick looked up sharply. "Human?"
"Briefly."
Snape was watching him now, still and sour. "You think it was an Animagus."
"I think," Cassian said, "someone got past every ward this castle has. Or worse, never had to break any."
McGonagall turned to the boys. "Did either of you recognise anything? See where it went?"
They shook their heads fast. Harry's eyes hadn't left Cassian.
"I tried tracking it," Cassian added, stepping past them. "Set up a flare trail. It bolted faster than expected."
Cassian glanced at Lupin, who hadn't said a word since he arrived, looking around grim. "Was Sirius Black an unregistered Animagus?"
That stopped every conversation cold.
Lupin flinched.
Snape made a noise that was technically a laugh but mostly just smug air. "Explains how he got out of Azkaban. And as I've already suggested to the Headmaster, someone inside this castle's helping him."
Cassian stepped between them before that got teeth. "Let's not start salivating over conspiracy theories just yet."
Snape opened his mouth, probably to do just that, but McGonagall cut him off.
"Rightly so." She turned. "Bathsheda, take the students to the Gryffindor common room, please."
Bathsheda nodded, already guiding Neville by the shoulder. Harry followed.
"Professor Rosier. Lupin." McGonagall's eyes flicked to both. "We're going to the Headmaster."
***
In the Headmaster's office, the Heads of House stood scattered near the desk.
Cassian was already by the perch, fingers casually teasing the phoenix's plume. "So, tell me, Headmaster, have you written your will yet? I'm wondering how many pairs of socks would tip the scales in my favour."
Fawkes clicked his beak and pretended not to mind.
Dumbledore didn't look up from his tea. "I plan to live a great deal longer, Cassian."
Cassian clicked his tongue, still fussing with the feathers. "Right. But if you happen to slip on a stray stair or choke on a lemon drop, I'd quite like to know where you got it."
McGonagall gave him a look. Snape rolled his eyes and turned away.
Dumbledore glanced up now, smile faint. "It was a gift."
Cassian raised both brows. "Was it now? From someone with a flair for eternal rebirth and dramatic exits?"
McGonagall cut in before that went sideways. "Can we focus, please?"
Cassian chuckled, dropping into the empty chair, "Right, big dog in the corridors. Grim-looking thing. Caught its leg, only for a second. It shifted. Human for half a heartbeat, then snapped back and vanished."
He glanced up at them all. "It moved fast. Too fast. Knew the castle better than I do. That's saying something."
Snape scoffed lightly under his breath.
Cassian ignored him. "I think it was Black. Lines up with the Fat Lady's door being slashed last week. Claw marks and all. Would also explain how he got out of Azkaban. Caught a flash of what looked like old prison robes. Stripes, thin fabric, leg was too thin. Starved."
Dumbledore let out a slow sigh. "Sirius knew the castle like the back of his hand. He and James were... quite mischievous in their time."
Cassian didn't bother softening his stare. "No time for a nostalgia trip. I don't care if they invented bloody stairwell limbo, he's inside, and he's targeting Potter."
McGonagall's mouth thinned. "Did he make a move?"
Cassian didn't look away. "He showed up near the kitchens when the boy was with me. Every incident so far was near Potter. If this isn't targeted, I'll eat one of Trelawney's scarves."
Snape leaned against the far bookshelf, arms crossed. "He's obsessed. Always has been. With Potter's father, then the boy."
Cassian pointed at him without turning. "You'll forgive me if I don't take obsession lectures from the man who's got a scrapbook of Potter's detentions."
Snape sneered. "At least I've never—"
"Enough," McGonagall snapped.
Flitwick cleared his throat. "The wards haven't sounded. That's what troubles me. If he's in and out without triggering them..."
No one spoke.
Dumbledore finally set his cup down. "There are no perfect defences. Not here. Not anywhere."
Cassian gave him a long look. "Then we've got two options. Patch the holes or spread wide to catch the rat crawling through them."
Sprout folded her arms, frown deepening. "Should we tighten security? Bring the Dementors closer?"
Dumbledore shook his head at once. "They cannot distinguish Animagi. I doubt they'd be of any use now."
She let out a breath, muttering something under it. "Bloody useless things."
Cassian glanced at her. "All bark and frostbite, those ones."
McGonagall straightened beside the desk. "If he is inside, we need a full sweep of the castle. Every inch. Every passage."
"He knows them all," Lupin said quietly, still near the door. "Even the ones Filch doesn't."
Snape snorted. "Finally decided to speak, have we?"
Lupin held his gaze. "Sirius and James mapped the place top to bottom. Hidden stairwells, back exits, trick doorframes. If he wants in or out, we can't just block the castle. He already knows every gap."
Cassian tilted his head. "So you should know them too, right?"
Lupin sighed. "Some. Not all. There were places even I didn't follow them into."
Snape glared at Lupin. "Help," He snapped. "It takes help to escape every detection."
"What are you trying to say?" Lupin said sharply.
Snape turned. "It is clear, isn't it? You're awfully quiet about the man who used to sleep in the same dormitory."
Lupin stiffened, but didn't bite.
Cassian rubbed his jaw. "Why in God's mailroom don't we have anti-Animagus wards tied to the entrances? Or a detector that screams when someone trots in on four legs?"
McGonagall cleared her throat, one of those polite, lethal coughs. "We did. For a time."
Dumbledore's eyes crinkled. "Too indiscriminate. The castle hosts owls, cats, kneazles, the occasional rat, Hagrid's menagerie, and..." he tipped his head toward McGonagall "...a Deputy who is, by Ministry leave, a registered Animagus. The old lattice treated every four-legged passage as a breach. We spent a term chasing Mrs Norris from alarm to alarm. And Professor McGonagall could not reach a broken staircase without waking half the portraits."
Flitwick nodded, wincing. "The alert web also misfired on transfigured supplies, brooms to beams, stools to span a gap, anything that shifted state within threshold."
Cassian flicked a look at McGonagall. "So the school turned the tripwires off... for you."
Her mouth thinned. "For the ability to do my job. And for students who require rescue at inconvenient angles."
Dumbledore folded his hands. "We narrowed the net, ports, external walls, certain vaulting, but Hogwarts is a living enchantment. Add too many bars and the music goes flat. So we rely on minds that can discriminate, portraits, elves, staff. It is imperfect, admittedly. It is also how no child is locked inside their own safety spell."
Cassian sighed through his teeth. "Right."
Dumbledore stood then, slow but there was steel in his expression now. "That's that. If Sirius is inside, we will find him. I'll speak to the portraits. The ghosts. The elves. Every corridor will be watched."
After the final points were made and the room thinned out with murmurs and closing doors, Cassian stepped toward the exit.
"Cassian. A moment, if you would."
He paused, turned. "Trouble?"
Dumbledore shook his head gently. "Not yet."
Cassian leaned on the back of the chair, waited while the rest filed out. McGonagall gave him a glance but didn't ask. Lupin lingered at the threshold, then vanished down the stairs without a word.
The door clicked shut.
Dumbledore looked up at him, quiet for a beat.
"Your Patronus," he said. "May I see it?"
Cassian blinked. "Bit of a weird time for a talent show, Headmaster."
"Humour an old man."
He sighed. "Alright."
He glanced at the ceiling. "Eh, it'll punch through, but the ghost upstairs could use a wake-up."
"Expecto Patronum."
He raised his wand. The tip lit up sharp, then flared.
Silver light burst from it, splitting upwards, each one sharp as if carved into the air. The shape stretched tall and broad.
(Check Here)
How can someone emit the aura of maybe later?
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