Prologue
A Horcrux. Voldemort had torn his own soul apart, mutilated it, to the point of doing so on accident.
After the Dark Lord came back during the third task of the Tri-Wizard-Tournament last year everyone either panicked or straight up denied his return.
And Dumbledore? He sent him back to his wretched relatives. For "protection" he said. What protection? The "powerful" Bloodwards that probably don't even work anymore since Voldemort used his blood in that wretched ritual?
He wasn't stupid, no matter what others thought. He read all kinds of books in order to survive the Tournament. In secret of course. Sometimes he even used his cloak to sneak into the restricted section and take some books with him. He hid them in his trunk when he wasn't reading them, so that nobody would find them.
That's how he found it. "Secrets of the darkest Arts". So what if he read it? He was in a deadly Tournament, he couldn't afford to be picky. And it sounded useful. It was useful. Just not in the way he intended. At first there wasn't anything that interested him and after the Tournament he forgot about it. That's why he accidentally took it to the Dursleys with him.
Luckily they didn't take his stuff this time, so he at least had his trunk in his room. So when he got bored one night and looked through his trunk to find something he could read just to find this book, well who can blame him for his curiosity?
And that's how he found it. The chapter about horcuxes. It didn't take long for him to connect it to the diary. It took a bit longer to connect it to himself, but that was mostly because it's never been done before. However, the parsel tongue, the "dreams", the pain in his scar whenever he's near Voldemort and Dumbledore telling him that Voldemort gave him some of his powers with the scar were pretty clear signs.
A Horcrux, a vessel for the Dark Lords soul, that's what he was. And Dumbledore knew. And he didn't deem it important enough to tell him. Because of course Dumbledore didn't, he needed to die after all, otherwise Voldemort would stay immortal. And wasn't that a depressing thought? He was raised to die. He was supposed to die.
But if there was something he excelled in, it was breaking the rules, doing exactly what he wasn't supposed to do. That, and surviving against all odds. He didn't know if it's because he loved rebelling, because of some twisted sense of revenge against Dumbledore or because that long suppressed Slytherin self-preservation finally broke out of the box he had shoved it into when he was sorted into Griffendor, maybe it's even the Horcrux. But he didn't want to die.
He didn't even want to survive any longer. He wanted to live, and he'd be damned if he didn't succeed. That is why, in a bout of absolute insanity, he decided some things had to change. He sat down on his desk, took a quill and a piece of parchment, because that is all he had in this prison that Dumbledore calls his home, and wrote a list of things to do.
1. Go to Gringgotts
Because, again, contrary to popular belief he wasn't stupid, he knew his parents must have owned another place to live in. He heard they only bought that house in Godrics Hallow in order to hide (and didn't that go well?). Plus Sirius had told him that he made him his heir. So he needed to go to Gringgotts and find out what exactly he owned.
2. Move into one of his properties (preferable out of the country)
After all, he knew the Blacks owned more then one property and thanks to Sirius he was the acting Head of House, at least he should be, since Sirius told him he couldn't take the Lordship due to being convicted , that's also something he needs to figure out what it means. And he really didn't want to be in Britain during the war.
3. Write a letter to Voldemort (with a new owl)
He needed to explain all this shit to him after all, if only so he doesn't try to kill him anymore. However, he can't use Hedwig for this since everyone knows how she looks like, thus, he needed a second owl. That talk did not go well but she saw reason eventually and agreed.
4. learn what he needs to know
5. buy what he's lacking
Because he's been ignorant for far too long and willing to bet Dumbledore kept other secrets from him, things that are common knowledge in the wizarding world , that nobody ever taught him, that he needs to know.
He looked at his list, finally satisfied, it's not complete but he can think about everything else later, when he's safe and gone.
He'll miss Hogwarts and his friends but he can always write them a letter later to explain everything and while Hogwarts was his first home he was also constantly in danger and that's just not an option anymore. Plus, he really does not want to see Dumbledore right now.
So he took out the worn out backpack he used when he attended primary school and put "Secrets of the darkest Arts" , his invisibility cloak and his last owl treats inside. He can buy anything else later. He put his wand in his pocket, went over to Hedwigs cage, freed her and opened the window. "I'm sure you can find me wherever I'll end up staying, girl." She hooted in confirmation and flew away. Now all he had to do was wait till midnight to set his plans into motion.
A few hours later the clock finally hit midnight. He took his backpack, put on a too big old cap to hide his scar and face and jumped out of the window. The landing was a bit rough but he didn't let it stop him. He left number 4 Privet Drive and continued to walk for a while just to be sure. After reaching what he deemed a safe distance and called the knight bus.
"Where to?" The conductor asked. "The Leaky Cauldron", he answered and payed the eleven sickles needed. He always made sure to have them with him where ever he goes since last year. After all one never knows when the night bus is needed. Like now. He went inside and prepared himself for the ride.