A/N: This fic is an Alternate Universe type of story. That means I have changed canon events, timelines, some characterizations, etc. to suit my wishes. Some of your favorite characters might not be the way you like them.
If this isn't your cuppa, then please be advised that there are over seven hundred thousand Harry Potter fan fictions here on FFn. Something is bound to suit you better.
Legal matters, effective for the entire story:
This is a work of derivative fiction. I own many copyrights in the world, but this is not among them, nor will it ever be. All things Harry Potter are the intellectual property of J.K. Rowling and all to whom she has given license. I'm just here because I like a good "What if".
"James! Lily!" Sirius bounced off the Anti-Apparition wards, landing solidly on his arse in the village of Godric's Hollow. He shook off the jolt and pushed himself up to his feet, tears half-blinding his vision. "Harry!"
Extending his wand ahead of him, in case James had put permissions keyed in to each of their magical signatures, he sprinted back to the cottage, leaping over the white wooden gate as it seemed to provide the only reflective surface on the nearly moonless night. He was able to gain entrance to the property this time and a part of his mind—the part that actually managed to get five N.E.W.T.s before leaving Hogwarts—noted that he'd been right about the wand signature and the property wards. It didn't occur to that part of his mind that the wards had been compromised. "James! Lily! Harry!"
There was no answer, just the sound of the autumn winds whistling through holes in the upper story of the small manor house, and the two broken windows he could see. His fractured heart was pounding and Sirius wanted to stop and howl like Moony. After all that hiding, and after making Peter the Secret Keeper—had he been killed as well?
"James! Harry! Lily!"
He didn't even have to push to get the door open, though he hated doing it. The smells that skirled to his nose were redolent with death and dark magic. His knees buckled, but he shook it off and reminded himself that he was an Auror, by Merlin's beard, and he wasn't going to falter.
The first body he tripped over was draped in black. He could smell blood—James must have got some effective hexes in, there. Maybe even a Reducto. Good job, mate, Sirius thought, not daring to speak out loud now that he was inside. The second body he tripped over was also draped in black and bound with something . . . something he didn't recognize. Maybe James and Lily had been experimenting in personal defense spells whilst he himself had been away?
The third body he tripped over was wearing trousers and a jumper of Gryffindor red. Sirius let gravity carry him all the way to the floor, his eyes welling with silent grief. Oh, he'd expected this, yes, but he hadn't truly been braced for the visceral punch. Prongs . . . Glasses askew and broken, James stared unseeing at the ceiling, his face frozen in the midst of a shout. Sirius called upon the training he had, the reflexes he depended upon, and felt for a pulse and for breath, but he knew. His inner canine knew.
Fury built up, like the pressure of waves on a beach, as Sirius gently closed James's eyes for the last time before setting the broken eyeglasses to rights. The latter was a futile measure, but it suited his sense of propriety. He took James's wand, tucked it in a pocket, and stared hard at his best mate before rising to his feet. I'll take care of 'em. Just like we talked about. I swear it.
The tears fell unchecked as he dashed up the steps to the upper floor.
The weak, frightened cry shattered his heart but it tugged him to the proper door, as did the scents brought in on moving air. Old leaves, more dark magic. Nappies. Lily. Harry.
Harry. There was no other voice as Sirius entered the nursery, wand in front of him at the ready. It wasn't as dark as it had been downstairs; the ambient light from the starry sky filtered through a haze of the mess that had been left behind.
He shifted and the toddler in the cot jerked, his little body falling on its bum just before Harry screamed with a thick, desperate sound. "Daddy?"
Sirius couldn't contain his sob as he lurched toward his godson. "It's Uncle Sirius. Harry. Uncle Padfoot."
The fourth body he tripped over was Lily's. She had crumpled to the floor, her face anguished but without any visible sign of her demise. Must have been an Avada, Sirius noted with that Auror part of his mind.
He locked the observation away and took a deep breath, remembering what James and Lily had said to him, not too long ago.
"Merlin, Pads," James had muttered. "We don't want it to happen, no, but a man's got to be prepared."
"So does a woman," Lily asserted, rolling her eyes but clutching their son against her as she stood, swaying back and forth as if she were a hammock. "And if the worst happens, we'll send a Patronus—"
"Lils, come on!"
"If the worst happens," James said, his voice louder than Sirius's own, "we'll have a bag packed in the pantry downstairs. Not a likely place for a Death Eater, right?" Lily snorted before nuzzling Harry and pretending that everything was fine. "The bag will have clothes, nappies if he's not trained yet, our will, and some other things. We'll have them all shrunken down for you to make it easy, all right?" James's eyes shone with desperate sincerity.
Sirius's throat clogged. "Easy?" he tried to say. It came out broken.
Lily nodded, her voice oddly soothing as she said what she felt she had to say. "Easier than you having to sort and sift, Sirius. Look," she went on, meeting his eyes over Harry's tousled head. "You were an entitled, self-centered prat when we were in school, but you've got over that, mostly, which is why we both wanted you to be Harry's godfather. I expect you to be there for him if he needs you. Acting like a good Auror, a good man. The man I know you can be. The man I've seen surrender everything materialistic for his principles. The man who will go beyond the bounds of magic for his friends."
"But remember you're a Marauder, too," James had added, trying to bring a smile to the heavy conversation. "Raise him to fly a broom. To find fun. To enjoy a little female challenge now and again."
"Do not mention girls, James!" Lily demanded with an edge to her voice.
"Only if she's smart like you, Lily."
Sirius scrubbed at his face, rubbed at his burning eyes to keep his tears inside, and joined in the more lighthearted teasing. "Give me my godson," he said, rising to claim Harry from Lily's arms. "Hey there, Prongslet. We're gonna give your parents something to really worry over, all right?"
And he had carried the toddler out to where his motorcycle waited, settling the pair of them on it with sticking charms before revving up the engine.
Lily's furious shouts could be heard through the entire village.
In the nursery, as October passed to November, Sirius nodded, his chest heaving in silent weeping as he gathered Harry next to himself. "C'mon, Prongslet. Let's get your gear and go home with Uncle Padfoot."
Harry was whimpering for his mum and dad, and Sirius almost lost it. Somehow, he gathered a happy memory to his mind. "Watch. I'm remembering the day you were born, Harry. Watch this." He called, "Expecto Patronum!"
A large dog, silvery and active, leapt from the tip of his wand. Sirius beckoned to it with his wand hand. "To Remus. The deer . . . are gone."
It was a code that could be said in front of anyone, as any Patronus communication had to be safe to do. But it broke his heart to make the devastating announcement with such tepid words.
"First, we get you safe, lad," he told his godson. "You're my boy and I've promised to do my damnedest for you. For your mum and dad. And I will."
"Mummy?" Harry looked around, straining to see over Sirius's broad shoulder as they left the nursery. "Daddy?"
"Bloody he—, shite, er. No. She's sleeping. Waiting for us on the other side. All right? You and me, we'll do our best until we see her and your dad again."
"Absolutely. But not tonight. Come on."
Sirius would never, in all the years after, know how he managed not to fall apart and scream, cry, break things, or go after Peter Pettigrew, who had clearly broken his vow as Secret Keeper. He would forever and always lay the blame—or credit—on the sacred bond of being a godfather. Only Harry's wellbeing could have priority over his burning desire for retribution. For justice.
It always would.