Timeline: OOTP, just after the Battle of the Department of Mysteries. This story is chiefly HP, but makes connections to Avengers/MCU later on. Intended as an introductory piece to a more even crossover.

Bella's shriek rang through the dank air, as the unspoken countercurse he'd prayed would save him died on his lips. Bella's curse - not the Killing Curse, surprisingly - knocked Sirius Black off his feet. A gasp from Harry, and Sirius felt cold wisps tickle his skin - the curtain? - as he flailed wildly, grasping at anything that would break his fall. The fall that took him through the crumbling archway, hearing Harry's anguished screams as he landed, flat on his back on hard stone.

Sirius lay on the ground, bewildered that he hadn't lost consciousness. The room he'd fallen into was completely silent. There was no noise at all, not even the merest susurrus of the curtain.

Gingerly, he pulled himself to a sitting position, and stared. There was no curtain. The faint whisper was in the air around him, but there was no material to make the rippling sound. There was nothing. No arch, no doorway. Nothing but bare, impenetrable stone.

But, Sirius thought, if I fell through... Then he gave a shuddering sigh. The Veil. The mystery of Death, Dumbledore had said, was in that room.

And Bella had known. As fascinated as she'd always been with dead and dying things, it was hardly surprising she'd be drawn to it. The glee he'd heard in her cracking voice was explained. She'd stood him up before the gates of Hell, and pushed.

Odd, he didn't feel dead. A ghost, then? The ghosts at Hogwarts were conscious, right? If he was a ghost, he could at least haunt Bellatrix for the rest of her miserable life.

Then, a mad idea occurred. Ghosts could pass through solid objects.

Even stone.

Sirius looked at the wall in front of him, marble-glassy, shimmering with an oily sheen, myriad hues wavering, shifting, disappearing from sight.

He stood up, and adopted the pose he'd so often used on Platform 9-3/4: relaxed, not a care in the world, not paying the least attention. Gently, he leaned into the wall.

Nothing.

He thought again. Ghosts remained behind because something held them. Who'd ever heard of a nonchalant ghost? He laughed at his own foolishness, and changed position. Holding himself straight, he marched purposefully into the wall.

It didn't budge. He put his hand to his nose (sore), and pulled his hand away (bloody).

It was almost black, the blood. Sirius placed the streaked hand against the wall, leaving half a handprint on the smooth surface.

Well. Maybe he wasn't dead, at that. The Bloody Baron's blood had always looked silver, and hadn't come off on any physical object he'd passed through.

There was too much he didn't know about this. He still might be dead after all. But a bloody nose was hope enough to go on with.

Sirius had never, until Azkaban, been a patient man. The excitement of rejoining the Order, of seeing his godson again, had made him careless. Reckless.

Not this time.

He looked about the chamber, noting a single passage going out, with the beginning of a stair. He shook himself off, and took it.

Author's Note: Thank you for reading! This is my first fic, and while it has been beta-read outside of FFNet, there may yet be some error-correcting or tweaks. Reviews much appreciated!