The small division between those who are good and those who choose not to be.
"Yes, but the world isn't split into good people and Death Eaters," said Sirius with a wry smile.
When they arrived on the scene, Sirius could already hear the screaming. He could smell burnt flesh coming from somewhere in the half collapsed warehouse in front of him and for the first time in recent memory he felt terrified.
He and James had been summoned from where they were staked out at a muggle bar to this dilapidated warehouse where four of the Order had been ambushed by Death Eaters.
"Be careful," James said to him, gripping his arm briefly before pulling his wand and charging into the building. Sirius nodded before doing the same.
Inside, the warehouse was sweltering. There was the crackling of flames somewhere but Sirius couldn't see through the smoke that was rapidly appearing.
His eyes were stinging before he thought to cast an impervius charm, hoping desperately it worked as well on smoke as it did on water. It wasn't perfect, but it would have to do. He didn't have much time to think of another charm before he was firing off hexes one after the next, barely even thinking, just looking long enough to make sure it was a Death Eater. One went down, then another and another. All stunned or knocked out. They weren't to kill the Death Eaters, not yet.
Even though the smoke wasn't affecting him as much now, the heat was becoming overwhelming. His leather jacket stuck to his skin, impeding his movement. He wanted to tear it off but he knew the second he tried, a wand would be at his throat.
He saw Moody moving through the smoke, strangely graceful, and Sirius immediately moved towards him.
"How many?" he yelled over the crackle of flames.
"Just three more," Moody barked in return. His eyeball was moving rapidly around in its socket. Sirius nodded and went off in search of the final Death Eaters.
It didn't take long. No sooner had he turned a corner than he saw a Death Eater making his way towards one of the unblocked exits.
"Immobilus!" he shouted and the Death Eater froze where he was standing.
"You're not going anywhere," Sirius muttered as he approached the Death Eater slowly, looking around him all the while.
He reached out his wandless hand and flipped up the white mask.
A younger, slightly distorted version of himself stared back wide-eyed.
"Regulus," Sirius gasped. "What are you doing here?"
"What does it look like?" Regulus hissed, all defiance and poisonous anger.
"You can't be one of them!"
"Oh don't act so high and mighty. Noble Gryffindor through and through, aren't you?" he spat. "You might like what the Dark Lord has to offer if you would give him a chance. He can take away your pain, Sirius," his brother said as Sirius backed away a little. Who was this person whose dark eyes were a little too wild? Where was the younger, naïve brother he knew? He struggled to hold his wand straight and steady. This was an enemy, he told himself but as he stared at his younger brother he couldn't help but have doubts.
"Sirius!" came a cry to his right. James was running towards him, seemingly unscathed except for an angry red gash across his cheek. His gaze flickered from Sirius to Regulus and back.
"It's going to collapse!" James told him as a burning rafter came shattering down as if on cue. "We have to get out of here!"
"You go ahead," Sirius told him. "I'll be along in a minute. I have to take care of this."
James looked like he was going to argue but only nodded before disappearing out the open door.
Regulus waited for James to leave before saying, "Sirius, I'm still your brother. Let me go."
"No. You're a Death Eater," Sirius said but his tone wasn't as confident as it should have been and he knew Regulus had noticed as well.
"Come on, Sir. If you don't, this building will kill us both."
Sirius ducked as another piece of wood fell from the ceiling. His eyes darted around, taking in the spreading fire, the open door.
"If I let you go," he said finally, "I never want to see you or hear from you again, do you understand me?"
Regulus turned towards Sirius once the spell wore off.
"You know," he said, "it's fine for you to disown me because I'm a Death Eater, but the world isn't divided into good people and Death Eaters, Sirius."
"It is to me," Sirius replied coldly. "Now leave."
Regulus ran out of the building, not looking behind him. Sirius apparated to James' moments before the infrastructure of the building collapsed in a cloud of smoke and dust.
Three weeks later Sirius received an owl informing him of his brothers recent demise. He stared at the parchment for a very long time but he did not attend the funeral.