For two weeks, Harry has toads following him to every class, to every meal, even to his dormitory at night. Hard as he tries, it's impossible to completely avoid them, and it's when he reaches under the bed for a lost quill that his fingers touch the reason why: it's dried out, but when he pulls it into the light it's easily recognizable. The dead toad has runes carved into the flesh of its belly and its back, and Harry groans, pulling out the second one from under his bed.

He walks straight to Snape's office, and when he enters, Snape is bent over a cauldron, focusing carefully on it.

"Is that Remus' Wolfsbane?" he asks as he enters, and Snape makes a tch of sound, but otherwise ignores him. Harry waits patiently until Snape sets his stirrer aside, and the man turns to stare down at Harry. "What do I do with these?" Harry holds out the dead toads, and Snape glances from them to the two toads that had managed to follow Harry into the office.

"Where did you get them?"

"From under my bed," he answers, letting Snape take one of them and examine it. Harry hadn't closely examined the runes on the toad's corpse, but Snape does so with deep focus, arching his eyebrows slightly.

"An odd concentration of resources for a mere prank," he comments dryly, reaching for the other toad. Harry lets him take it, and Snape pulls a Size 1 cauldron out of a cupboard, setting it on the floor with a clatter. He drops the toads into it, and then he takes a fairly large, stoppered jug from a top shelf, pouring it into the cauldron.

There's a rather sickly, bubbling sound, and Harry does his best not to retch as he watches the toads melt into the hissing drink.

"What is that?" he demands.

"Acid," Snape replies. "The easiest way to destroy them." He points with one pale finger to the toads, who are no longer focused on Harry and are instead wandering the room. "It's a very old ritual, fiddly and... Disgusting. It affects non-sentient and semi-sentient beings to converge on a target."

"How?"

"One feeds its anchors the target's hair, blood, or flesh. Said anchors are dessicated, properly carved, and placed in decent proximity to the target. Then, one simply sits back and watches the convergence." Harry stares at Snape for a few long moments: the man had delivered the information simply, with a slight shrug of his shoulders.

"That's disgusting," Harry says.

"But effective," Snape points out, and he kicks the cauldron to the side. "Go away."

"Thanks," Harry says awkwardly, and Snape ignores him, looking back to the Wolfsbane on his desk. Sighing, Harry makes his way out of the room, shaking his head. He looks up the ritual that day, though: the ritual had been used by druids, and had once been called the Banding of Beasts. It had once been used to impress Muggles in ancient times, or to scare them - with the right anchors used, any semi-sentient creature could be compelled to follow a target.

There aren't explicit instructions as to the ritual in the old text, which isn't that surprising - most of the more dangerous magic in the library is talked about vaguely so that students don't attempt it - but it involves a lot of focus on lunar cycles and fiddly work with potions ingredients and different forms of magic.

It's an extremely odd thing to use to just make him a bit uncomfortable, and reading through the texts available, Harry can't understand why Gudgeon would send toads to follow him.

He keeps his eye on Gudgeon the next few days, and it's a Wednesday evening when Harry and Hermione are walking up from Hagrid's house that they see Gudgeon at the gates of Hogwarts. Harry and Hermione pull themselves under the Invisibility Cloak, rushing as fast as they can to see her accompany her visitors to the gates.

"You're sure they're ready?" a Scottish woman asks.

"Completely," Gudgeon replies. "The walls will be utterly destroyed. We'll get them out quite easily, ladies. I'll see you." The two women nod their heads, and they leave through the gates: Hermione and Harry watch as Gudgeon locks them closed again.

"Do you think she's going to try and blow Hogwarts up?" Harry whispers to Hermione, and he feels her shake her head.

"You can't. In the 40s, they got really paranoid about Muggle bombs from the war. Professor Flitwick was telling me about it one day - there are all sorts of charms so that you can't bring Muggle explosives over the threshold, and missiles and bombs dropped from above are just rerouted into the sea." They follow Gudgeon slowly up to the castle, slipping into the great hall for dinner, and Harry is pensive as he sits with Draco.

"What's wrong with you?"

"If there was one structure in Wizarding Britain that you could blow up to scare the population, and it wasn't Hogwarts, what would you choose?"

"Uh, the Ministry of Magic?" Theodore suggests.

"St Mungo's. Diagon Alley."

"The Knight Bus station is Aberystwyth."

"Hogsmeade." The Slytherins take it for a hypothetical - they eagerly drop into conversations about strategy and history, and they're all so focused on the discussion they don't realize that Harry doesn't join in. He listens to them as they talk back and forth, going from one target to another. None of them strike him as quite correct.

He looks up to Gudgeon where she sits at the table, chatting energetically with Flitwick, and he drums his fingers on the table in front of him.

He barely eats that night.

But he sleeps. Oh, Merlin, does he sleep.

---

Harry wakes with a harsh gasp at four thirty in the morning, grabbing tightly at the arm that had touched him, but he stops short as he realizes who the arm belongs to. "Get up, Potter," Snape orders cleanly, and he does the same to Draco, shaking the boy quickly out of his sleep. "Don't bother getting dressed - just put on your dressing gowns and your shoes. Now." Snape sweeps from the room, and Draco looks blearily around.

"Wha's goin' on?"

"Not sure," Harry says, putting on his glasses and grabbing his wand, slipping it into his dressing gown's pocket. "Come on, Draco. I think this is serious." They move into the corridor, which is full of confused, sleepy Slytherins, and prefects snap orders from the common room, ordering people into lines.

They move up ot the great hall in a big mass, and Harry can see the Hufflepuffs are being ushered in the same direction: the Ravenclaws are already in the room, and Flitwick is running back and forth, Conjuring chairs and beds for them to settle in. There's anxious, quiet chatter between the students, but it's obvious no one knows what's going on - the prefects look as pale, worried and tired as everyone else, and it's plain they have no inside knowledge.

Rain pounds loudly on the castle roofs, the enchantment looking more like that of the lake than the usual night sky, and Harry flinches along with every other student in the room as lightning flashes across the enchanted ceiling, followed by a loud blast of thunder.

Hermione beelines straight for Harry when she enters the room, and Harry reaches for her hand, holding it tightly as they look to the doors. Dumbledore is dressed in a silken purple nightshirt, a thick, fluffy dressing gown of a similar colour pulled over it, but despite the rather whimsical look of the outfit, he's as serious as Harry has ever seen him. His gaze doesn't twinkle in the slightest, and his lips remain pressed together as he looks around the room.

"Is everyone here?" he calls.

"All of the students, Headmaster," McGonagall replies. She puts her hand on Filch's shoulder, stopping him from leaving the room. Harry watches as they argue for a moment, and then Filch goes over to Flitwick, turning away from the doors. Other teachers filter into the room - Burbage, Sinistra, Vector, even Sybil Trelawney, who doesn't look as if she's stepped into the great hall in six lifetimes.

When Hagrid brings Fang into the room, pushing him to go and sit with the Weasley twins, Harry gestures for him to come over. "What's happening?" he asks hurriedly, and Hagrid just shakes his big, shaggy head.

"Dementors, Harry. They've left Azkaban."

"What do you mean?" Hermione asks sharply. "They can't leave Azkaban - they don't. There's an agreement."

"They've left," Hagrid says. "And they're headin' North. That's why we want you all in here. Safe, like."

"Where's Professor Gudgeon?" Harry asks, looking hurriedly around the room. He feels sick as he realizes the woman is nowhere to be seen, and he runs over what he'd heard her say that night. They'd get them out. That's what she'd said. They'd get them out. "Oh, my God."

"What?" Hermione asks.

"They're not just blowing things up," Harry says. "They're blowing up- They're not blowing anything up. Structural damage, Hermione. Chad Arnett's explosives in Diagon Alley didn't blow up the street or anything - they blew out walls." Hermione stares at him, her eyes flicking over his face, and he sees understanding and horror dawn on her face.

"They're going to break him out." Harry's blood feels cold in his veins, and he runs across the room, slipping to a stop in front of Snape and grabbing at his sleeve. Snape is in mid-conversation with Remus, the two of them talking rapidly, and Snape stares down at Harry's hand on him as if Harry's touch is going to give him cholera. "They're going to break him out," Harry says urgently. "The dementors are gone, because they're going to break him out."

"What the Hell are you babbling about, Potter?"

"The dementors have left Azkaban," Hermione says sharply. "Gudgeon, she was friends with Chad Arnett, who attacked Diagon Alley in December. They're going to blow out some of the walls in the jail - they're going to break Lockhart out."

"Oh, fuck," Remus says, and then shoves his hand over his mouth, looking horrified with himself, but Snape doesn't seem to hear him. "We need to-"

"Come," Snape orders, and Harry and Hermione follow after the two teachers, ignoring the protests from Frank Richelieu and Percy Weasley as they run out of the great hall and through the corridors. Snape snaps out a spell that breaks the door before them off their hinges, and Remus just kicks it down and out of the way, like it's normal - they step inside, and Harry looks around the empty set of staff quarters. There's only bare pieces of furniture, nothing on the walls - even the ugly fruit bowl on the table is empty.

Harry and Hermione keep close to the two professors as they walk back towards the great hall - for once, Snape isn't continuously putting jibes in Remus' direction, and the two of them speak quietly and seriously, using defensive terms Harry wishes he could understand.

Burbage, Flitwick, Sinistra and McGonagall are in the entrance hall, and Snape joins them. Lupin rushes to find Dumbledore with Hermione following him, but Harry hovers, listening to the staff members talk.

"We can't strengthen the wards against these," Flitwick says. "This isn't an attack by wizards - dementors are barely on this plane, Severus. If they come here, Patronuses are our best defence."

"Twelve Patronuses against several thousand dementors," Sinistra says sarcastically, her melodic voice ringing in the hall. "A perfect balance."

"There are other defences," Snape agrees, "We can-"

"If you dare suggest Fiendfyre-"

"It's one of the only things that destroys them!" Snape says urgently, and McGonagall lets out a sharp little noise of frustration.

"And it destroys everything else, Severus. Would you have the castle destroyed!?" Harry's never seen teachers argue like this, and the spectacle is fascinating despite the situation, but before he can listen any more Snape notices him.

"Go, Potter." Harry opens his mouth to refuse, but there's a loud pound on the entrance hall door before it's thrown open. Harry stops short, staring slack-jawed at the two figures standing in the wet darkness, soaked to their greying, greenish skin: they're dressed in rags, blood seeping through the white cloth from their chests and their backs, and when they step forward it's the unnatural, clumsy step of something no longer alive. Harry's seen Muggles try to emulate it in horror movies Dudley's secretly watched in the middle of the night, but this is so much worse: he can smell the rotting stink of the two bodies as they shuffle forwards, their limbs at odd, broken angles. They move like strings are holding them up, just barely.

"Oh, Merlin," Burbage cries out, staring at the two monsters in horror. "That's- Severus, that's-"

Harry recognizes them from their photo in the Gazette, even though Padraic Fenton's eyes are sunken deep into his head, even though Darla Fenton's hair is coming away in sickly clumps from her scalp.

"Stupefy!" Snape casts sharply, and the red beam hits one of the zombie-like figures, but it doesn't so much as stumble - the magic hits it and seems to just disappear.

Harry heaves in a breath, grabbing for his own wand as the figures shuffle forwards: all the teachers are casting spells, but none of them seem to have any effect, and Harry gets himself ready to cast. He can see their eyes, now: the two of them have white, empty eyes, and Harry's horrified to realize as they come closer to him that they're breathing. Their chests rise and fall in slow, shaky breaths that make quiet groans of sound, and Harry's faced Voldemort, but he hadn't scared him like these two living corpses do.

Harry stumbles back, down and towards the hall of staircases, but the two of them follow him: they're focused on him, only him.

Silhouetted by another shot of lightning, Harry sees the first dementor out on the hill, and he realizes with a sick shock down his spine that it's focused on him. Gudgeon had done the same ritual again, with the Fentons as anchors: the dementors are coming after him.