Title: No Fortress Is So Strong

Summary: In 1981, the two Potter sons had their fates switched, and Nicolas Potter became a famous face. But there are those that know the truth, that the real Chosen One was the younger child. The Slytherin. Now, two brothers share a destiny.

Disclaimer: This story is based on characters and situations created and owned by JK Rowling, various publishers including but not limited to Bloomsbury Books, Scholastic Books and Raincoast Books, and Warner Brothers. Inc. No money is being made and no copyright or trademark infringement is intended.

Notes & Caveats: This is a rewrite of the fanfiction story Slytherin Serpent. The premise was originally thought up in 2004, rewritten in 2006, and rewritten again in 2009. This is the only complete version.

Many, many thanks go to my intrepid team of beta readers: Micah and Salazire, who are thorough and clever and absolutely fabulous.

"When brothers agree, no fortress is so strong as their common life." ~Antisthenes

Chapter One: So it Begins

In July of the year 1979, the Potters had a son.

They were both just twenty years old at the time, still children themselves really, and the Years of Terror (dubbed as such by the Daily Prophet) were still at full strength. Little Nicolas Potter was a surprise, the result of one night of unprotected passion, after one of many close calls.

They called him Nicolas after Lily's maternal grandfather and Evan after his mother's maiden name. And from the moment he was born, he was their life and their reason for living, and their ultimate goal was to provide a calm world for him to grow up in.

Nicolas Evan Potter was an eclectic mix of his parents' genes – he had James's mother's dark brown eyes, Lily's deep red hair, and the pale, pale skin common to redheads. When he was a little older, he even got a few of his grandfather Nicolas's large, pale freckles in the summer months.

Lily and James thought he was perfect, and couldn't love him any more than they already did.

Unfortunately, there was a war.

When Lily first discovered she was pregnant, the Potters discussed their options. Neither wanted to leave the war effort to others, but neither did they want to leave their son an orphan. It was decided – eventually – that they would take turns. Lily would watch their son for a few days while James aided the war effort, then he would return and Lily would take his place. To this end they asked one of their best friends Peter to perform a complex charm on their home in Godric's Hollow – the Fidelius Charm, a powerful spell that would ensure their home's complete invisibility and inaccessibility to anyone who wasn't told by the Secret Keeper – Peter – where it was.

And for several months, this worked wonderfully. Since the charm was on their home and not on the Potters themselves, they could leave and return at will, and still be completely protected within their home's property line.

Then one night Lily became pregnant again.

Seven and a half months later, Nicolas's younger brother was born six weeks premature at the end of July in complete silence. Terrified and sobbing, Lily watched as the Hogwarts Nurse gathered up her silent and unmoving son and a Portkey and rushed him into Hogwarts while a panicking James helped clean her up enough to follow. When they arrived, their tiny baby lay under extensive monitoring charms, clean and dry now and with a thick thatch of wild black hair.

"Oh," Lily said, laughing through her tears. "He's going to look like you!"

They called him Harry James, and they fell in love with him at once.

Then they realized he was one of two possible children of Prophecy, as Albus Dumbledore told them that night.

He resided in Hogwarts – in a specialized, hidden room – for nearly a month, until he was grown enough to be taken home and cared for by his parents. Even after he grew, however, he was still a little…strange.

Harry cried a lot. Not loud and obnoxious screaming, but quiet tears even more terrible for their lack of sound. Lily and James drove themselves spare trying to calm him down and dry his tears, offering him all manner of toys and comfort, but it didn't help. He never gained the weight he needed, never flourished as did his brother.

When Harry was born in such frightening circumstances, his parents made a decision they'd already been contemplating for months. With two sons their responsibilities had doubled, and with one son a probable target of the Dark Lord, in August of 1980 the Potters vanished entirely into hiding. For over a year, only a few select people had any knowledge of their whereabouts.

Until October 31st, 1981.

The Potters celebrated Halloween early that year. Two-year-old Nicolas gleefully accepted several bites of chocolate cake, and fifteen-month old Harry sat swinging his legs in his high seat, talking solemnly to his father in incomprehensible mumbles as James nodded and hmmed and spooned mashed potatoes into his son's mouth. The potatoes made his already thick mumbles even less understandable, but no less intent. When James didn't seem to be paying attention, Harry added expansive gestures to the mix.

Harry luckily didn't mind not having chocolate cake, because Lily and James were careful to feed their youngest son only healthy foods as Harry rarely liked to eat at all. If he had any chocolate cake, he would refuse dinner, and according to James, if he had enough room for chocolate, he had enough room for more carrots.

However, despite this strict regime Harry still suffered failure to thrive.

Regardless, Lily had taken Harry upstairs early, his arms and legs limp and his head resting on her shoulder, while James sat Nicolas down on the rug in front of the fire and set to entertaining him with simple flashy charms. A few minutes later, Lily returned and smiled indulgently as her redheaded son tired rapidly, yawning widely. James tucked him into his side and stroked his hair as he fell asleep.

For a long time, it was quiet and peaceful, and then James heard the creak of the old wooden gate.

"Is that Peter?" Lily asked curiously, lifting her head.

"Yeah, must be," James said, lifting Nicolas away from his side and handing him to his mother. The toddler mumbled a bit and relaxed again in her lap, and James rose to his feet and headed for the door. He passed a window facing the front of the house, and that was the only thing that saved him from an instant, violent death.

Outside the window, a tall figure in a black cloak – not Peter – strode directly towards the front door. James froze in surprise and confusion, and the figure raised his wand and obliterated the door. There was a deafening crunching sound, and jagged pieces of splintered wood flew everywhere. The walls shook and the windows shattered. Lily cried out and Nicolas screamed in fright.

"Lily," James gasped, fumbling for his wand. "Lily, take him and go!"

Lily staggered to her feet, clutching her terrified son. The figure outside stepped forward.

"Go, Lily!" James yelled, finding his voice. "I'll hold him off!" James raised his wand, hearing dimly through the rushing in his ears his wife's footsteps up the stairs, where an emergency Portkey sat hidden in a secret cupboard.

But James didn't even have time to say a single spell – while his mind was still half on Lily running up the stairs, a flash of green light enveloped him. James's eyes closed and his body folded into itself; he sprawled long-limbed and graceful upon the floor.

As she reached to top of the stairs, Lily turned and saw her husband fall. She screamed, a desperate, terrified, anguished scream, and clung harder to her sobbing son. She turned and lunged into the boys' room, where Harry was standing waveringly in his crib, eyes wide. There were rapid footsteps on the landing; there was no time to grab Harry and make it to the Portkey.

But perhaps there was one thing she could do…

With a wave of her wand as the door flung open, she changed Harry's hair and eye colour to the only colours she could in the split second that she had. The wind of the flung door whipped her long hair forward over her shoulders. She dropped Nicolas in the crib beside his brother and whipped around, eyes narrowed, wand out. She would defend her sons until her dying breath.

The Dark Lord Voldemort stood before her, tall and thin and darkly cloaked. She couldn't see his face.

"Step aside," he whispered to her, voice like a breath of bitter wind.

"No," she said, "take me. Take me instead. Not my sons. Please, have mercy. Don't hurt my sons."

"Step aside, you silly girl. Step aside."

"NO!" Lily screamed. "Please, oh god, please have mercy and take me instead!"

"So be it," came the terrible whisper, and that dreaded flash of green lit the room. She couldn't step aside – her sons were behind her. Lily closed her eyes and let it hit her.

She sprawled limply to the ground, her hair spread out in dark crimson ripples like a pool of blood.

Voldemort kicked her body away and surveyed the two babies before him. He wasn't sure which one was which, but it didn't matter. He would kill them both. He levelled his wand at the first redheaded child, staring up at him silently. Voldemort cast the spell.

He didn't even see it hit the boy, much less himself. He only felt a terrible ripping sensation, the remnant of his soul being torn from his body and catapulted away. Behind him, the house imploded, flames shooting high into the sky. Harry Potter was flung backwards onto his back by the curse, a thin stream of blood running down his face. Taller and stronger, Nicolas managed to remain upright until a tall glass vase on a high shelf exploded when the house began to crumble. Shards of glass flung in all directions, and a piece sliced shallowly into Nicolas's face as it spun past. Nicolas shrieked in surprised pain and fell backwards, hands going to his face. The movement rocked the crib, and then the shuddering house knocked it over, spilling both boys onto the floor.

After a moment, the house shuddered to a still silence, barely standing. Nicolas's face was covered in red. Harry was barely clinging to consciousness, laying silently on his back and covered in chunks of plaster, bits of wood, and a thick layer of white dust.

As the house rumbled into silence, a single, solitary cry rose and fell, wavering, full of pain and terror and anguish.

Several hours later, long after Nicolas's cries had faded away into silence, the house groaned loudly and threateningly as enormous footsteps sounded on the stairs. Miraculously, the house remained standing even as the owner of the footsteps reached the landing.

Nicolas whimpered from where he lay beside his mother's body, the blood on his face flaking off as it dried. There was a gasp, and Hagrid crouched to pick him up.

"Nicolas," he breathed, choking on tears. Nick whimpered again as he was moved, twitching restlessly as he was settled into the crook of a vast arm.

Hagrid knelt down beside the body on the floor, gently reaching out to straighten her and close her bright green eyes. He was still for a moment, tears trickling down his face.

Then he reached out and snagged a blanket from Harry's fallen crib. The motion caught at the crib itself and turned it sideways, exposing Harry's still form. Hagrid felt his heart clench. The littlest Potter…

Hagrid reached out, gently grasped a large chunk of plaster and lifted it away. To his delighted surprise, the movement caused a pair of dark eyes to slide open dazedly. Hagrid gave a cry and hurriedly blew away the dust, gently picking Harry up.

"You're alive," he rumbled, over and over. "You're both alive."

He gathered another blanket and wrapped one around each of the boys. Harry was silent and a little limp, and Nicolas was clearly in pain.

"Come on, then," Hagrid said in his deep, low voice. "We'd better get yeh ter 'Ogwarts, and get yeh both looked at righ' away."

He gathered them up into his arms and gingerly stood, wary of the groaning floorboards, and made his way as lightly as he could out of the house.

He was just contemplating how he was going to get them both back to Hogwarts when there was a roar and a screech, and an enormous motorbike dropped out of the sky. Hagrid stared.

A tall, black-haired man leapt off the bike and staggered, looking devastated.

"No," he moaned. "No, James. Lily! James! NO!"

"Sirius," Hagrid managed. "Sirius, 'm so sorry."

"Hagrid," Sirius choked. "Are they…are James and Lily…?"

"They're gone," Hagrid said hoarsely. "But the boys are okay."

"Nicolas and Harry?" Sirius asked, dazed. "They're…they're still alive?"

"Righ' here," Hagrid said, nodding at the toddlers in his arms. Sirius gave a hoarse, choked cry and stumbled towards him, arms already reaching out, sobs bubbling up from his throat. He touched them with trembling hands, ran his fingers down Harry's lethargic arm, choked back a moan at the dried blood on Nicolas's face.

"Wh-why does Harry have red hair?" Sirius choked out. "Wh-what a silly thing…"

"I don' know," Hagrid said, baffled.

"G-give them to me, Hagrid," he managed hoarsely. "I'm their Godfather – I'll take them."

"Dumbledore wants 'em at 'Ogwarts," Hagrid said apologetically. "An' I think they need t'be looked after, righ' now. By a nurse, like."

"Yes, you're right," Sirius said, seeming to force his voice to be level. "That's a good idea. Here, look, take my motorbike. It'll get you there faster."

"But yeh love tha' motorbike," Hagrid said, aghast, but Sirius was already shaking his head.

"Take it," he said firmly. "They're more important."

"Well, all righ'," Hagrid said, grateful for the help. "Thank yeh, Sirius."

"Take care of them," Sirius whispered, and then bent to give each boy a kiss, carefully avoiding the bloody gash on Nick's face.

"I will," Hagrid vowed, and swung his leg over the bike. It came to life with a bone-shaking roar, startling both boys awake and into tears.

"Bye, Harry, Nicolas!" Sirius called hoarsely. Hagrid waved and the bike sprang aloft.

Sirius didn't wait for them to disappear into the distance. His face hard, he neatly turned on his heel and vanished with a crack.

"Which one got hit, Dumbledore?" Minerva asked, voice hushed. "Which one got hit by the Killing Curse?"

Dumbledore stared down at the two sleeping boys before him, remembering the prophecy. Both boys were born near the end of July – the 31st in Harry's case, the 29th in Nicolas's – but Dumbledore knew which one it was. He could feel it in Harry's mind, the terrible fright and hurt. Even now he was quiet and worryingly still.

In contrast, Nicolas was restless in his sleep, whimpering with terror and distress. His newly healed face had a terrible scar, starting in his forehead and extending down over his eyelid and onto his cheekbone. It was still red and irritated, but would eventually fade to a thin white line. Harry also had a scar, a funny zigzag shape on his forehead, like a lightning bolt.

Harry had a terrible destiny before him, Dumbledore knew. The Dark Lord had marked him as his equal…

"Oh, Lily," Dumbledore breathed inaudibly. "Smart, amazing Lily. If you'd been a pureblood…"

She'd tricked the Dark Lord. How and why, Dumbledore didn't know, but she had. He'd known what she had done the moment he'd seen two little boys with identical red hair and dark eyes in Hagrid's arms. He'd been forced to reluctantly alter Hagrid's memories of the event after returning Harry's colouring back to normal. No one else could ever know.

She'd given Harry a chance, and Dumbledore would honour that, though it put little Nicolas in deadly danger and likely would not get him any thanks from either boy. But it had to be done.

I'm sorry, Nicolas, Harry. I am condemning you both to lives that aren't yours…

"It was Nicolas," Dumbledore said, with a voice of certainty. "Nicolas survived the Killing Curse. He is the Boy-Who-Lived."

"Oh," Minerva said, gazing down at the older child. "It's a miracle."

"Yes, it is," Dumbledore murmured, eyes on the second, smaller child, who lay so still and quiet. "A miracle, indeed."

"Who will raise them now?" Minerva asked quietly. "After Sirius…and Lupin certainly can't."

"I'm afraid we will most likely have to separate them," Dumbledore said softly, "unless we can convince Lily's sister to take them both in. But my instincts rarely lead me astray, and in this case they are telling me we will have to find alternate arrangements for little Harry."

"Lily's sister?" Minerva asked, aghast. "Albus, you cannot truly…Lily hates...hated her sister, she told me many times. You cannot, certainly…not a Muggle? He would be dead in a day!"

"I will invoke a set of Blood Wards," Dumbledore explained. "As long as he is in a house with his mother's blood kin, no one will be able to touch him."

One dull, grey Tuesday evening, twenty four hours after the Potters were killed and their son destroyed their murderer, Albus Dumbledore quietly mounted the steps to a children's home in London. Cradled in his arms was a black-haired baby, fast asleep.

For a long moment, Dumbledore simply stood there, remembering a similar moment earlier that evening when he rang the doorbell of a house in Surrey, while two-year-old Nicolas dozed restlessly on the porch. He'd watched from the shadows as the door had opened begrudgingly to show a heavyset man with a moustache. He'd stared down at the toddler at his feet in abject surprise, then looked around suspiciously. He'd shouted a few times out to the dark street, threatened to call the police on charges of abandonment, but when no one answered his shouts he had at last picked the child up and retreated into the house, where he would undoubtedly call to his wife and then find the letter detailing Nicolas's circumstances.

Dumbledore found himself loathe to do it a second time, with circumstances so uncertain, but he forced himself to gently set the warm bundle on the ground and step away. Just before he Apparated out of London, he waved his wand. There was a loud knocking sound on the door, and the doorbell rang stridently, and he turned on his heel and vanished away.

The door opened. A curious child peered down at the wrapped bundle in the moment it took for a caretaker to arrive. Then there was a gasp, and two hands reached out and lifted the bundle off the cold ground.

There was a note that fell out of a fold of the blanket, just a single piece of paper folded in half.

His name is Harry James Potter, it read in slanted script. He was born 31 July, 1980, and he was orphaned on Halloween.