When Sirius came to, he was lying face-down on the cold stone floor, his eyes shut, and his head throbbing. He hadn't the faintest idea where he was or how he got there, but he didn't have the energy to open his eyes, so he just lay there, listening for any sounds that might tell him where he was, but an eerie silence surrounded him.
He tried to remember what had happened before he passed out. At first there was nothing; his mind was a blank wall. Then, like a river bursting through a dam, everything flooded into his mind all at once. James, Lily, Harry…. and suddenly he didn't want to remember. He wanted to make it stop. But it didn't.
He remembered walking away from Godrick's Hollow, and straight into a lamp post. He remembered deciding to find Wormtail to demand an explanation. He could remember, with sickening detail, pushing the door of Wormtail's hiding place open, and finding the place untouched; no signs of a struggle, not even a picture frame out of place. He could remember standing there, in the middle of the disturbingly tidy living room and coming to the horrible realization that the information hadn't been tortured out of Wormtail; Wormtail was the spy, all along. He remembered hunting down the boy he once thought of as a friend, to demand an explanation for what he did; a justification for the unjustifiable. He remembered finding him, cornering him, yelling at him…
And then everything was a blur. Not because he couldn't remember now, but because he was delirious then. There was an explosion of some sort… he remembered that much. An explosion, and lots of shouting. And then it went black.
A shiver of cold ran down Sirius' spine, and he heard an odd rattling noise - something eerily inhuman. He opened his eyes slowly, but all he could see was the stone floor his face was pressed against. Slowly and painfully, he pushed himself off the floor, raising his head wearily, and finally, looked around him. He was in a room. A small, cold room, with no furnishings and a large metal door that had no handle. High above him, a candle burned, dripping its hot wax onto his leg that was so numb, he didn't even notice the wax until he saw it. It took him a while to figure out where he was; it was not until his eyes fell on the rows of tally marks scratched into the wall opposite him that he realized he was in Azkaban.