(Unedited, subject to light revision and sentence restructuring, story shouldn't change)
(Authors note before beginning, I am writing under the assumption that Sirius and Dumbledore are both secondary secret keepers under the fidelius charm, thus they know the secret but cannot knowingly reveal the secret. I don't know if its canon but it is here. thanks for reading. Also taking some other liberties with magic)
Dumbledore had been having quite the pleasant afternoon, despite the current state of the Wizarding World. He had just finished a lovely meal courtesy of the Hogwarts house elves and was enjoying some sweets from the bowl on his desk when a distinctive pop indicated the arrival of a house elf.
Before the poor thing could speak though another more urgent visitor arrived in the form of a black dog patronus.
"Potters in danger, he knows" was all it said before blinking out of existence.
Without a word he was gone, not even a sound made, as he apparated away with a masters skill.
...
It was like any other night at the Potter's, James and Lily spent plenty of time doting on their son Harry, and Lily was just getting ready to lay the child down for the night. As she goes to move up the stairs of their quaint home she hears a hurried knock on the door.
Seeing as only people they trust should be here, Lily was quick to answer the door, only to find a worried Dumbledore on the other side.
"Lily there is little time you and James must take Harry out of here, He knows where you are and He is coming." Dumbledore was using his commanding voice, not wanting them to hesitate for a moment, and they didn't
James had heard everything from the living room and had already grabbed coats for him and Lily, putting the coats on and wrapping Harry in Lily's, they were ready to go in seconds.
"How Dumbledore?" James asked, needing an answer.
"I don't know I thought Sirius was the secret keeper, but it was his patronus that brought the warning." Dumbledore stated quickly not wasting anymore time and leading them through the door.
A whispered "Peter" was heard from Lily before all went silent.
And then hell itself seemed to fall from the sky, as fiendfyre in the form of a myriad of snakes descended upon the trio. Apparently Voldemort wasn't very happy with his uninvited guest.
Working with the speed and grace his year mastering magic gave him, Dumbledore is quick to deflect the burning death above their heads, causing it to decimate the area in front of the house before quickly dispelling it. Leaving nothing but the darkness and an eerie silence.
The moon breaking from the clouds gives light to the snake and skull in the sky, signifying that they were trapped, at least when it comes to apparition.
The lull in combat was short lived, as Dumbledore proceeded to shield the Potters as they ran behind him for their lives and that of their son. All the while a light show proceeded behind them.
"You wont save them Dumbledore, you can't!" Spat the now visible cloaked form of Voldemort.
"Tom you failed the moment I knew you were coming, leave them be, just fight me."
"And that is where you are wrong, oh so very wrong, Dumbledore, I may not be happy that you are hear, but a great wizard keeps contingencies." The Dark Lord sounded smug, as if victory was already assured.
Almost two dozen crack and pops and there are now twenty Death Eaters surrounding Dumbledore, hurling every curse and unforgivable in the book at him, a true cascade of sound and color lights the night as Dumbledore defends against such an overwhelming surprise attack.
Using his wand he created a dome of earth to block the unforgivables and within the next five seconds he had blasted the rock out and into the surrounding Death Eaters.
Five seconds was all Voldemort needed, he apparated right to the Potters, still within sight. A wave of his wand and both parents are thrown on their backs. wands flung in the distance, while Voldemort used a levitation spell to lift baby Harry to him.
"Please don't hurt him, don't hurt my baby! Kill me instead! Please I beg you!" pleads Lily, tears staining her face as her child's life hangs by a thread in front of her.
"No! Not them me! Please, I'm begging you take me!" James screamed his face painted with panic.
And now Dumbledore could see the heartbreaking sight, casting the counter curse for Morsmordre would let him get there sooner, as then he could apparate, but time was not on his side. A sick feeling hit his stomach as the first curse hit the child, not the killing curse, no Voldemort wanted to watch the suffering of James and Lily as they screamed for mercy.
A wail fills the air and empties hearts as Harry screams from the cruciatus curse pulsing through him, His parents watched in horror at the sight before them, but only for a moment.
Whatever spell they had been hit with it didn't matter, as they saw their son about to be hit again with Crucio, James threw himself in front of the spell, falling to his knees in pain while Lily pulled Harry from Voldemort's levitation spell.
"Almost there" Thought Dumbledore, sweat upon his brow as he works to dispel a Morsmordre cast by the Dark Lord himself. If only he weren't so old maybe her could have sprinted the few blocks to help, but his only hope is to undo this curse and hope its not too late.
But it would be too late, shielding her son, Lily is hit with a Cruciatus curse bringing her down to her knees. Voldemort grabs her hair yanking it back until he can aim his wand at the bundle in her arms.
"Avada Kedavra!" a green flash, the color of death, and it was over.
As Lily opens her eyes she isn't greeted with the dead son she was expecting, she saw a crying and scarred but very much alive son. Turning behind her she is greeted with nothing but an empty cloak and a retreating cloud of black smoke barely visible in the deep of the night. Looking over at James who is picking himself up off the ground he looks confused, but relieved.
In an instant Dumbledore is by their side, and in the next an out of breath Sirius, looking at first fearful and then relieved as he sees his friends and son very much alive.
"Oh thank God, you made it" dropping down on his knees Sirius grabs both of his friends by the back of their heads and pulls them in close, bringing his forehead to theirs, he just takes a moment to appreciate that his friends are here and alive, after a moment he looks down at Harry, sadness etching his face as he watches the still crying boy but relief that he still has the air in his lungs to cry,
"What happened Dumbledore?" James asks, the confusion is writ on everyone's faces, now turned to the old headmaster for an explanation.
"I do not fully know James, it would seem Voldemorts spell reflected back on him, as to the why I will need more time, for now we should get little Harry to Saint Mungos, not to mention the both of you."
Standing they all got ready, James and Lily went and retrieved their wands. While Sirius stood and dusted himself off. A mischievous grin soon gracing his charming face.
"Once you are cleared at Saint Mungos I'll have to introduce you all to my son" Declared a Sirius Black with a seriously shit eating grin on his face and a serious lack of decorum considering the near death experience his friends went through.
But it definitely broke the tension as both Potters give him a "WHAT!?" before they all apparated away, deciding to continue the conversation while at Saint Mungos.
And so Voldemort was defeated, the story of his dark crusade cut short by a boy little over a year old.
It may have been the end of the war but not for the Potters, their family was just getting started, and Sirius was about to learn what it takes to be a father.
...
Authors Note
This was honestly tedious but fun, trying to make canon stuff fit and molding things to fit my narrative i wanted to tell. I wanted to explain why Harry still lived even though his parents didnt die. Sacrificial protection isnt one of those spells that is clearly laid out, I read somewhere that its either possible or could be possible to block other unforgivables and still create the spell necessary for the protection without having to die. I also read ( might have been a fanfic i cant remember) that the act of trying to plead for the life of your loved one offering your own is a pretty big component. So pretty much between two parents taking unforgivables and pleading for their sons life while offering their own in exchange, I felt like it was enough to protect Harry from Voldemort, whether its strong enough to last into his school life you'll have to see.
Next chapters are going to be some slice of life, growing up, character building. Finally introducing the main character as more than a nose grabbing babe. This is what I am excited about.