A/N: Yes, this is genuinely a zombie apocalypse Severitus fic. I know that the apocalypse genre is not everyone's cup of tea, but I hope at least a few of you out there will like it :) This is a canon divergence starting after fifth year, so all wizarding world/characters/events established in canon prior to then still exist. There will not be horcruxes. The dynamic between Snape and Harry here is a comrade-like sort of mentorship, less parental than the It Takes a Village series was, but still centred around their relationship as well as the obviously apocalyptic plot.

The sickly sweet smell of decaying organic matter clogged his nose. The man ignored it as he urged the spluttering motorcycle he had hijacked forward just a little more, swerving out of the sudden reach of yet another creature. Every now and again, he was forced to use his wand to fend them off. Somewhere in the distance, the sound of breaking glass preceded several long screams of terror. If the man were anyone else, he would have winced. Instead, he schooled his expression into one of detached purpose.

Everything had all gone terribly wrong.

For once, the Dark Lord had created a monstrosity beyond his ability to control. He had summoned his Death Eaters to a ritual circle in Devon the evening before. They had all been surprised and dismayed to learn that their leader intended to perform a Necromantic dark ritual with unknown results during a new moon. Despite their reservations, they had no choice in the matter but to participate and watched in horror as the night and ritual progressed to a dangerous whirlwind of magic that everyone present, including the Dark Lord himself, was powerless to stop. Considering that said ritual was performed by someone in possession of strong magicks and a pronounced dark taint on their soul to begin with…

Severus tossed a strong blasting curse over his shoulder mid-swerve and turned onto Privet Drive, skidding to a halt in front of Number 4 just as the engine began dying out. He jumped off and carelessly allowed it to topple over behind him. He was panting, having been running or driving at dangerous speeds for the past several hours. There was no time to catch his breath, however, so he pounded on the front door. Potter better be home, or I'll—

He heard running behind the door, and the sound of someone cursing. There was a thud, and a shriek farther down the hall. The door swung abruptly open, a harried-looked Potter holding it ajar while a large man nearby hurried forward, reaching out to shut it again.

"Are you mad, boy?" the man yelled. "Shut that door!"

"It's my teacher, he can help," Potter argued back.

Severus shoved his way inside past the large man, who was shouting about "not wanting any more of that lot around here" and Potter let go of the door, which was promptly slammed shut by the man.

Things were a bit tight in the entry hall, so Severus drew himself up to his full height and glared down at the blustering man while Potter backed into the corner, clearly concerned about the scene that might unfold. "Mr. Dursley, I presume. Terrible to meet you. Now, if you would be so common as to barricade the door."

He strode down the hall, Potter squeezing past Dursley and following closely at his heels.

"Sir? What's happened? Are those things out there really zombies? Did Voldemort make them? Have you talked to Dumbledore yet?"

Ignoring the teen, Severus beelined for the Dursleys' telly and turned it on to the news.

"Frantic reports from across the nation claim that creatures which appear to be animated human corpses are attacking anything that moves." The video feed changed from a white-faced reporter to clip after clip of the creatures summoned by the Dark Lord's ill-fated ritual, with location stamps in the corner. Bristol. Carlisle. Oban. Weymouth. Inverness. Cork. Cardiff. Preston.

Severus didn't bother to switch off the telly as he turned away in disgust. He caught sight of movement at the top of a staircase as a pudgy, fearful face looked down from the landing. "Mum? What's happening?"

The woman sitting on the couch, whom Severus hadn't bothered to look at (no need to sour his already terrible day with the sight of Petunia Dursley,) clucked. "Dudders, come here."

The teen, Potter's cousin Dudley, thumped down the stairs and hurried to his mother. They began whispering together.

"Professor?"

He looked down at Potter, who was staring at the telly. Severus glanced at it, but didn't see what had caught the teen's attention. It was only a video of London—

He sat down heavily on the edge of the coffee table, fingers tightening around his wand as he watched the creatures breaking into the Leaky Cauldron. It was portrayed on the bloody news, as if…

"You!" he spat to the quivering mother and son pair behind him. "Can you see that pub?"

"What? Of course we can," Petunia stuttered, then narrowed her eyes at him. "Wait, are you—"

Severus cursed and stood, pacing back and forth in the tiny parlour.

"What is it?" Potter asked, tracking his movements with concerned green eyes.

"The wards are falling," he said. "The Leaky Cauldron has muggle-repelling wards on it. It should not be visible at all in a recording, to muggles or wizards. The creatures are interfering with the magical field."

"What are those creatures?" he asked.

Dursley lumbered into the room. "It's something to do with your kind, isn't it?"

"I believe muggles die quite easily," Severus said, glowering at him. The man quailed slightly.

"So they are zombies?" Potter pressed, not deterred.

Severus shot him a glare. "Zombies are a muggle myth."

"So what are they? Inferi?"

Severus refused to be impressed that Potter would know what an inferius was. "Similar. They are corpses animated by magic, but they are under no wizard's control, and they are not preserved. Regardless of what one wishes to name them, they are infecting others."

"Sounds like a zombie to me," Potter muttered. Everyone ignored him.

"Look here," Dursley said, "I don't know what you're doing in my house, but me and my family aren't getting involved in whatever queer business you lot have cooked up."

"Of course you aren't," Severus scoffed. "It is much harder to keep five people alive than two."

"What–?" Potter began.

"Do you have your wand?" he interrupted.

"Yeah," he said, pulling it out of his back pocket as a trio of shrieks came from the muggles.

"Get anything else you can carry easily that will help on the road."

Potter wisely didn't ask any more questions, only running upstairs. Severus was faced with three terrified, angry muggles.

"You're taking him, then?" Petunia asked.

"Unfortunately."

"How… how do we stay alive?"

"I would not worry about it overmuch," Severus said, glancing up when Potter emerged with his invisibility cloak tied into a bundle around some items on his Firebolt and his owl on his shoulder. "You will not last long anyways."

Potter trotted at his heels as Severus headed for the front door. He paused at the last moment, glancing over his shoulder. Impatiently, Severus stopped and tapped his foot.

"If you have finished taking your time," he groused.

"We're just gonna… leave them?"

Severus raised one dark eyebrow. "Do you want to bring them along?"

"No," Potter said flatly.

"Then hurry up." Brandishing his wand in front of him, Severus opened the door and stepped out onto the Dursleys' front lawn. Potter followed a moment behind, shutting the door. Half a second later, pounding footsteps could be heard from inside, and the lock clicked shut.

There were no creatures within a 50 metre radius. Still, he cast a basic shielding charm around himself and the teen.

"Where are we going?" Potter asked.

"Hogwarts."

Harry's knuckles were practically white as he gripped his wand, eying the creatures coming nearer to them. He glanced at Snape, but the man only looked as stern and fierce as he had ever since Harry first saw him that day.

The first sign that anything had been wrong came early that morning with Aunt Petunia's screams when she looked out the window and saw a zombie in the backyard. Everyone had rushed downstairs to see what was wrong, and watched in confusion as it wandered away.

Then the phone began ringing off its hook, and the next two hours were spent trying to wrap their heads around the fact that the zombie apocalypse had happened and trying to secure the house. When Snape appeared at their front door, Harry had been ready to collapse in relief. A person he would have happily never seen again only twelve hours ago was suddenly someone Harry couldn't wait to get inside the house. After Sirius died, Harry had blamed Snape for ignoring his warning. It took a few weeks for him to realise that he was just shifting the blame to someone else because blaming himself—the person really at fault—hurt so much more.

He still didn't like Snape, but Snape was a wizard, and a powerful one at that.

"Do not let them touch you," Snape said tightly.

Harry blinked, brought out of his reverie, and nodded. He adjusted his grip and slid one foot back slightly in a battle-ready position. "I'm not going to get in trouble for underage magic for this, am I?"

Snape scoffed. "If the Ministry can get Aurors through this horde to come and rescue you, they are welcome to have you. It would mean they are more competent than I give them credit for." He glanced down at him briefly. "So no."

Harry rolled his eyes, wondering if it would kill the man to just give a straight answer for once without wrapping it in an insult. Then the first zombies were upon them, and all thought was lost to the red haze of battle.

"Incendio!"

"Sectumsempra!"

"Immobulus!"

"Confringo!"

"Bombarda!"

"Depr— oh, hell—" Snape grabbed Harry and pulled him uphill when he saw another wave of zombies coming from a different direction. "Cave Inimicum!"

A dome-like shield settled around them, and zombies began butting up against it. Harry panted, hands on his knees. Snape stood straight, eyes focused and bright as a thin bead of sweat trickled down his temple from the effort of holding up the shield. They were surrounded on all sides by a small but determined horde.

"Can we apparate out of here?" Harry asked.

Snape shook his head. "Because the creatures are animated by dark magic, they disrupt the magical field."

"The what?"

Despite everything, Snape still took the effort to give Harry a very disgusted look. "Do you pay no attention to magical theory?"

No, he didn't. He cleared his throat and shrugged, wondering how long the respite would last until Snape was forced to drop the shield.

"Potter, use a gouging spell to create a trench around us."

Harry wasted no time. Ignoring his exhaustion, he circled around the edges of the shield, blasting a deep, circular trench into the tarmac. As soon as he was finished and jogged back to Snape's side, the man dropped the shield with a shudder. The zombies, suddenly able to move forward again, all tumbled chaotically into the trench. Snape started blasting fire into it, and Harry was quick to copy him.

Harry continued filling the trench with flames as Snape used well-placed curses to pick off the ones who hadn't yet fallen in. It took several more sweaty, heart-in-throats minutes to kill (re-kill?) the last of the zombies.

They stood back to back, breathing hard and looking around at the mound of corpses surrounding them on all sides. Hedwig, who had flown up to the upper branches of a tree some metres away when the fighting began, returned to his shoulder with a soft cry. He absent-mindedly stroked her feathers. Snape, with one last exhausted wave of his wand, conjured a bridge over the trench and piled-up zombies so they could get past them without risking infection.

They walked over the bridge (a simple, slightly rickety wooden contraption that was probably as much as the exhausted professor could manage) with little fanfare, not wasting the energy to banish it afterwards.

"We need to find shelter for the night," came Snape's voice, slightly raspy.

Harry agreed. "Where?"

Snape shrugged one shoulder as they continued walking. There was some sort of building up ahead.

As they got nearer, they saw it was a little bed and breakfast tucked into a bend of the country lane they were travelling down. Rather than heading straight north towards Hogwarts, Snape had gone west. When Harry asked why, he'd been given a nasty sneer and a lecture about how "there are seven million people in London. They had already seen how this magic spreads by contact, and know that it has already reached town. Did he really have such a death wish? They would have to go around the city," so he had shut up and followed along.

Now standing before the B , they observed it closely for signs of zombies or even any people at all. Everything seemed calm, but that didn't necessarily mean anything. After staring at it contemplatively for a few moments, the professor marched determinedly up the front steps. Wand at the ready and forcing Harry to stand behind him, Snape rapped the front door sharply with his knuckles. The door was locked, but a man opened it at their knock.

"Are you infected?"

Harry watched Snape physically bite back a sarcastic retort before simply saying, "No."

The eye visible through the crack in the door narrowed, and then he stepped back and allowed them inside. He shut and locked it behind them, and Harry helped him to drag a table in front of it as Snape half-sat, half-fell into a chair. Harry noticed that his hands were trembling slightly. Magical exhaustion. Harry didn't know too much about Healing, but he recognized the symptoms from their disastrous trip to the Ministry to "rescue" Sirius.

"Where do you two come from, then?" the man asked.

"East," Harry said when it became apparent that Snape wouldn't answer.

"Just you and your da?"

Snape jerked his head up from where it rested in his hands.

"He's not my dad," Harry said hurriedly, grimacing. "He's my teacher."

"Oh." The man looked between the two of them. "Fight many crawlers?"

It's been one day, and already we're developing slang? "Too many." He sank into a chair a suitable distance from Snape, who was still looking slightly murderous at the assumption that he was Harry's father.

"We don't have much food here," the man said.

"Do you have anything at all?"

The man left and soon returned with a small tray of biscuits and other pastries. Snape took out his wand and duplicated the amount tenfold. The man gasped and staggered back.

"Snape…" Harry said, trailing off as the man raised an eyebrow.

"Gamp's law, Potter. Food can not be conjured or transfigured from another item of different substance. One can duplicate what one already has, but it cannot be made out of nothing. We must take advantage of what we get." He reached for a scone with one hand and pulled out a potion vial with the other. Magic replenisher. He downed the potion quickly, taking a bite of the scone afterwards to mitigate the taste.

The muggle gaped at them. "Was that… magic?"

Harry looked accusingly at Snape, who ignored the muggle and replied to his glare.

"I believe the statute of secrecy is the least of our concerns. The structure of both worlds is already crumbling. And if you think no one saw the flashing lights from our fight earlier, you're more the fool than even I expected you to be."

Before Harry could even decide which of that myriad of revelations to respond to, Snape had put away a second pastry and stretched out on one of the tables. Harry knew that the magic replenisher had a nasty side effect of knocking you out stone cold for a few hours while it refilled your core, so he wasn't surprised.

"I do hope you'll keep us alive until morning," Snape said, nodding at Harry's wand (which he still held vaguely at his side) significantly. Thirty seconds later, soft snores were coming from the man's rather large nose.

The stranger and Harry looked at each other for several long, awkward seconds.

"Biscuit?" The man asked weakly.

Severus woke feeling much better than when he'd gone to sleep. He wasn't unused to long days filled with lots of magical output, but fending off creatures almost constantly throughout the day after being part of the Dark Lord's insane ritual the night before (and getting no rest afterwards, as the whole thing had taken from dusk to half an hour before dawn) had drained him. Fortunately, years of pulling double duty as a professor and a Death Eater and spy during both wars had expanded his magical core and trained it to bounce back quickly.

He sat up, glancing around the cramped shop. The muggle man was sleeping, sitting in a chair, leaning against a wall. Potter was half-asleep, but sat cross-legged facing the door with his wand in his hand. Severus reluctantly got off the table (Merlin, but he was getting too old to be living rough like this).

"I am only thirty-six," he reminded himself.

"Huh?" Potter said, rousing from his stupor and looking over.

"Get some rest," he said, knowing that the teen was probably also fairly exhausted and would need his energy to fight when they went back on the road. Perhaps they would stay here for the day. His own magic was mostly replenished, but another day's rest wouldn't hurt. He could also outline a more detailed plan than the haphazard one he'd concocted while running from creatures (he refused to call them zombies as Potter stubbornly insisted on doing) the day before.

With that thought in mind, he figured he could afford a few basic wards around the property. He cast a few now, making them extra strong at the door and other points of entry.

The food was still on the table, although somewhat reduced. Potter must have had a go at it, then. Good. They would both need their strength in the days to come.

He nabbed an apple, wincing as he sat and thought about being forced to endure the brat's dubious company for at least several days more. When he woke, Severus would send a note with his owl to Dumbledore.

He found a glass behind the counter and filled it with water from the tap. He drank the whole thing right there, then refilled it and returned to the main area. The muggle remained asleep as Severus passed him.

At first glance, Potter was nowhere to be seen. After a quick spike of fear, however, he found the teen by looking under the tables. Apparently he felt more comfortable there than in the open. Sneering, but not saying anything, he sat in a chair several feet away and searched his pockets for some parchment to write on.

Albus Dumbledore,

I have Potter. He is alive and safe. We have begun travelling by foot to Hogwarts. Apparition is impossible. The creatures interfere with the magical field. I also have reason to suspect that they can bring down wards.

They are not terribly difficult to kill. Like an inferus, fire is effective. Potter has been able to hold his own. Far be it from Severus to compliment a Potter, but he knew Dumbledore would want to know how the teen was holding up. His relatives are still in Privet Drive.

If you could send someone to get him, it would be most appreciated. I doubt the two of us will survive each other any longer than we could survive the creatures. There. If someone came to get Potter and escort him through the horde to Hogwarts and safety, Severus could continue west to return to the ritual site and investigate more about the origins of these creatures.

Severus Snape

Letter finished, he set it aside and rubbed his temples. He could feel the bubbling warmth deep in his chest as his magical core replenished itself. From here onward, he shouldn't need to worry about draining himself that badly again. It was the ritual the night before that had mostly done him in, so he was fairly confident that his condition wouldn't deteriorate like that again.

As for Potter… the boy was young. While that meant his core wasn't fully developed yet, it would be easier for him to bounce back. He also believed that, while Potter was a terrible student and had survived this long because of luck, the teen did have more raw power than many of his peers.

Severus found himself considering going west with Potter. They would still go to Hogwarts afterwards, but a detour to investigate… no. Better to get the Boy-Who-Lived to safety first.

He gritted his teeth. The more time that passed, the less evidence he'd be able to find. The magicks would be harder to trace, and the scene could be tampered with. It would take weeks to get to Scotland by foot, and although he could move faster by himself on the way back, there would almost be no point by then. If only he had trusted the boy to fate and the rest of the Order, he could have already taken care of it. But no, Severus had made a promise over a decade ago, and his priorities wouldn't change now. As soon as he'd realised what happened and that Lily's son was unprotected in a Muggle suburb, he had immediately jumped into action.

"Still here, then?" a voice asked. Severus glanced up to see the muggle man awake and looking at him pensively.

"Apparently," Severus said.

"The boy explained about magic," the man said.

Severus inwardly cursed. "What did he say?"

"Not much more than what you showed," the man shrugged. "Some people can use wands and cast spells. You two are wizards. You're his teacher from wizard school."

"That's what he said?" Severus asked, wishing he had something stronger than water.

"Yeah," the man said. "Say, I don't suppose you'd want to stay here? That magic could sure be useful."

Severus shook his head. "We have to keep moving." He took a sip of water, as if to excuse himself from explaining further.

The man shook his head, standing up with a groan. "Suit yourself. I'm getting too old to be fighting for me life all the time." He left the room, and Severus stared after him. The whole world's at war, now.