Acknowledgements: Buffyverse characters are the creation of Joss Whedon and Mutant Enemy. Potterverse characters are the creation of J. K. Rowling.
Best Laid Schemes
The best laid schemes o' mice an' men,
gang aft agley.
— Robert Burns, To a Mouse
Prologue: November 1, 1981
Sirius Black watched from the shadows as Professor Dumbledore turned and walked away. He watched the old wizard pause at the end of the street, take his silver Put-Outer from his pocket, and click it once. He saw the twelve balls of light return to the street lights of Privet Drive. The restored lights revealed the tabby cat that was Professor McGonagall as she slunk around the corner at the other end of the street. He heard Dumbledore's murmured "Good luck, Harry" before the Headmaster turned away for the last time, and vanished with a swish of his cloak.
Sirius snorted. "Good luck, my arse!" There was no luck waiting for Harry in that house. He'd known what Dumbledore planned to do with Harry, now that James and Lily were dead, and there was no way he was going to let his godson be raised by those Muggles. He'd met Petunia Evans, and the idiot she'd married. He knew what dreadful parents they were, and he knew how much they hated the very thought of magic. There was no way in Hell that he'd let them raise Harry.
He had let Hagrid take Harry away from the ruined house in Godric's Hollow because he knew that he would never win the argument with Dumbledore. He never had, in all the years that he'd known the man. So he had developed his own method of doing things that he knew the Headmaster wouldn't agree to. It was summed up by the simple motto, "It's easier to get forgiveness, than permission."
He'd put his own plan into action immediately. It had started with a trip to the west coast of America. That was about as far away as he could go, and still make it back to England in time. He thought that Australia or New Zealand would have been better, but they were just too far. California would have to do. He'd found the child there: about Harry's age, same size, with the same tousled hair. His spell would work best if there was already some resemblance between the two of them.
It had taken a simple spell to render the baby's mother unconscious. Another, gentler one, was performed on the child to keep him quiet while Sirius whisked him back to Little Whinging.
Sirius hadn't only trusted the shadows to hide him and the child from Dumbledore and McGonagall. He made sure that his invisibility cloak was wrapped around them both when he carried the baby up to the front of the house and laid him on the porch beside Harry's basket. The old man had some things to learn about stealth. He'd be surprised if none of the neighbours had called the power company to report that the street lights had gone out. You'd never catch a Marauder drawing attention to himself that way.
Sirius unfolded the baby's blanket, spreading it out across the porch. He lifted Harry from the basket and laid him on the blanket beside the boy.
The spell he used was one that he and James had discovered during one of their late night research sessions in the restricted section of the Hogwarts library. It was tricky to cast, but it was one that they had found dead useful, many times. Better than Polyjuice for disguising someone. There was no awful potion that had to be drunk, and the effect would last until the right counter-spell was cast. When done properly it exchanged one person's appearance for another's. When Sirius was finished, the boy he had brought from California looked just like Harry, right down to the lightning shaped cut from Voldemort's curse on his forehead. Harry looked just like the boy.
Sirius placed the boy into Harry's basket. "Sorry to do this to you, fella," he whispered, "but you'll have a better life here than Harry would. You won't be doing any accidental magic to upset these Muggles." He chuckled. "The wizarding world is going to be shocked in a few years, though, when they learn that their Boy Who Lived seems to be a Squib." He tucked the blankets around the baby, he didn't want him to catch cold, and then he rewrapped Harry in the boy's blanket.
"Let's go Harry," Sirius whispered to his godson, as he picked him up. "I've got to get you to Sunnydale." Such a nice sounding name. It would be the perfect place for Harry Potter to grow up, safe, in perfect anonymity. No one could hurt him there, because no one would know that he was there. No need for a Fidelius to hide this secret. Another old saying came to Sirius's mind: "Two people can keep a secret, if one of them's dead." He was the only one who would know about this substitution. "Your new momma's going to be waking up soon, from that spell I put on her. Don't want her to think that her baby's been stolen, now do we? You'll be fine there. You'll live in a nice house. Not a big fancy one, but its nice enough, and I watched your new momma long enough to know that she'll love you. You'll be raised by parents who'll treat you as their very own, because they won't know that you're not. You'll grow up believing that you are Alexander Harris, far away from any of Voldemort's Death Eaters.
"And after I've got you safe into your new home…" Sirius's voice went cold. "…I've got a rat to kill!"
For ten years Sirius Black languished in Azkaban prison. Ten long years with only two thoughts to sustain him: the knowledge that Harry was safe, and that the rat who had really killed James and Lily was dead.
But the knowledge that Harry was safe was a happy thought. The Dementors sapped it away, leaving only his doubts about what could go wrong. Would the substitution be discovered? Would the Muggle family that he'd placed Harry with treat him properly? What if he had some mundane accident or illness: something a mediwizard could set right in moments, but that Muggle medicine was unable to cure?
After ten years he started to hear whispers. News came slowly to the prisoners of Azkaban. None came from the Dementors, but sometimes new prisoners brought news about what was happening in the outside world, or Ministry officials would let something slip when they came to interrogate someone. The whispers that Sirius was hearing seemed to confirm his fears. Harry Potter had started classes at Hogwarts. Harry Potter was the youngest Quidditch Seeker in a century. Harry Potter foiled the Dark Lord's plan to use the Philosopher's Stone to restore himself…
Somehow, his substitution must have been discovered. A Muggle couldn't do all those things. Even a Muggle-born wizard wouldn't be able to do all those things. Only a child as talented as the son of James and Lily must be would be able to do such things. Who else could have stopped Voldemort, while only eleven years old? Who else could have been such a great Quidditch player, at such a young age? Even if, against all odds, the child he had chosen had turned out to be a Muggle-born wizard, he couldn't have accomplished all that. It had to be the real Harry!
Dumbledore. It had to be Dumbledore. He must have somehow discovered the substitution, and gotten Harry back. That was the only explanation that made any sense. Of course, he wouldn't have told anyone: not let it slip that, for a time, Harry Potter had been away from his control. How long could it have been before the substitution had been discovered? Days? Months? Maybe even years. It might even be that Dumbledore had never learned who had done it.
When the time came, a year later, that he discovered that Peter Petigrew was still alive—and worse, at Hogwarts with Harry—Sirius had nearly forgotten what he had tried to do to protect the infant Harry Potter. The Dementors had taken nearly all of it away. When he remembered it at all, it was only his fears of all the ways that it could have gone wrong that came to his mind. In those moments he resolved to never tell anyone what he had done. If he ever encountered Dumbledore again, he'd only talk about it if the old wizard brought the matter up himself. He'd never tell Harry. It was better that Harry never knew that he might have had a life away from those Dursleys…