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Sirius Black stared morosely at the damp wall of his small cell as another tortured shriek rang though the haunted halls of Azkaban. He ignored it; whoever's throat it had come from more then likely deserved every second of this. Besides, one learned how to not hear such things after a while. If you listened, it would go on, forever and ever, causing you to grow mad. Mad as everyone else in this little slice of hell.
Sirius shuddered as he heard the half sane, high-pitched mutterings of the woman in the cell next to his. The whispers of the insane perpetuated the walls of Azkaban, giving the prison a sick sort of half-life. He shivered as the stale air developed a sudden chill, which found its way past his bones and into his very soul. Memories best left forgotten began surfacing from the depths of his mind.
The man's grimy features hardened into a scowl. Dementor…. Came the thought, full of loathing. With the long ease of practice his form flowed and shifted into another; that of a large, shaggy, black dog with matted fur. A few moments later the being passed his cell, its breath rattling as it passed in and out of its mouth. The mouth that you hoped never to see if you still valued your soul.
It paused for a moment outside of his cell, sensing a half foreign presence within. The things tattered robes hung like shroud about it, covering the clammy, decaying mockery of flesh beneath. The dog tensed, his fur on end, tension visibly filling every muscle. The Dementor let out another rattling sigh and moved on. But in its wake it left Sirius with in a memory.
The screams of injured and dying Muggles filled the air as the street was torn asunder beneath them by an angry incantation. He ignored them, concentrating on one thing; the despicable, rat like man 15 feet away from him. "You'll pay Peter for what you did! You'll pay for Lily and James' deaths!" Sirius shouted, pointing his wand at him. His eyes were wild with anger and hate, his handsome features were distorted with it.
Pettigrew's face paled further, if it was possible. "D-Don't kill me Sirius! Please d-don't. I had to! It was them or me. Don't you understand, He had all the power." Peter pathetically whimpered, stealthily waving his wand.
"You should have died for them. It would have been the honorable thing to do!" He hissed, advancing on him. Sirius quickly cast a spell, which Peter barely avoided.
A second later, a ghastly look of triumph crossed Pettigrew's face. He raised his wand and shouted the necessary words; a flash of brilliant blue light covered the scene, knocking Sirius back and hiding Peter from sight for a few precious moments. Moments that changed everything. The light cleared and Pettigrew was gone. All that was left was a finger where he had stood. And a rat. A rat that squeaked in fear and dashed into the sewers, leaving a tiny, almost imperceptible trail of blood behind.
Ministry vans began to arrive on the scene, wizards and witches jumping out as soon as they stopped. Sirius stared at the spot where the rat had disappeared and made a vow that one day he would kill Peter Pettigrew for his treachery. Even if it was the last thing he did, he'd avenge the deaths of Lily and James Potter.
The dog's head jerked up as it was freed from the memory. A moment later he surged back into his true form. Sirius gave a bitter, barking laugh that verged on insanity. "How Snape would love to see me now. Moldering away in this place." He muttered. "He'd love to see what I've sunk to."
He gave another laugh. "But he won't! He never will. Never, never. And that rat, Pettigrew; he'll never see it coming. No, he won't! He thinks himself safe while I'm here. Locked away. Locked away from the light of day!" Sirius Black said shrilly, giving a slightly manic giggle.
"But he isn't! He never will be until I am dead! One day I will escape! And he will die! Of course he will. Because all I must do is wait. Wait for my chance. Wait and wait, biding my time. I have a lifetime after all." The maniacal gleam in Sirius Black's eyes became brighter.
"I can afford to wait."