Sirius and Regulus switch places, after Sirius finds out Regulus betrayed Voldemort. When Sirius is killed in Regulus' place, the Black heir decides he'll pay back his brother's sacrifice however he can. When James and Lily die, that means taking in Harry Potter, his brother's godson. Can Regulus raise a baby Harry alone? Can he thwart Dumbledore's machinations?

July 15, 1981

Regulus fidgeted nervously and looked around the dingy flat. It was small, takeout containers littering every available surface, only two tiny windows lighting the room. He nearly jumped as the door banged open and turned to face a man he hadn't seen in two years. Sirius was wrapped around a rather buxom brunette. He hadn't even noticed Regulus as he stumbled through the doorway kissing his conquest. If he hadn't been so nervous, Reg probably would have laughed. Typical Sirius. Instead he settled for clearing his throat and taking a couple steps forwards. His brother turned his dark head towards him immediately. "R-regulus?" Sirius extricated himself from his date and squinted towards him. "What the hell are you doing here?" The confusion on the elder Black's face shifted into disgust and Sirius nearly snarled at him. "Get out. I have no business with slimy little snakes."

Regulus flinched at his older brother's tone. The sleazy woman laughed gratingly. "I really need to talk to you Siri." The twenty one year old looked shocked. Reg pressed on. "I need your help. Please Siri, I want out." Dark blue eyes narrowed in suspicion. Reg plastered on his most pleading face. The one Sirius could never say no to when they were little. Sirius sighed and nodded before turning a charming smile on the woman watching them. "Sorry, looks like I have other plans." The woman seemed affronted until Sirius leaned in and whispered something in her ear. With a giggle, she pulled him in for a long kiss, then flounced out the door satisfied.

"So what's this about? Why the sudden change of heart Reg?" Sirius' tone was carefully cold, Regulus recognized it as one their father used when he meant business. Reg took a deep breath and pushed up his left sleeve. "I was marked after graduation. Mother and father were so proud. I was finally living up to their expectations." The ones you left to get dumped on me, he added silently. "They made us do…stuff. It was awful Siri. All those people. I- I don't like muggles, but what we had to do…" He trailed off, forcing down those horrible memories. "Then the Dark Lord asked me to help hide something. Something important. I let him borrow Kreacher." Sirius' normally expressive face was blank. "I'm not sure what it is, but I'm positive it's valuable. I could get it." Reg took a deep breath. "I could get it and pass information to you for Dumbledore. Please Siri, I can't do this anymore." To his embarrassment, he felt tears pricking the corners of his eyes. Sirius held himself stiffly, looking so hard at Regulus that the young man wondered for a moment if he had learned legilimancy. Sirius must have found whatever he was looking for, because he relaxed and nodded. "Okay Reg."

September 8, 1981

"Siri, he'll be going after the Potters and Longbottoms soon." Regulus winced as Sirius turned deathly pale. "They're under fidelus. He can't find them." Regulus nodded. "He's looking for them though," privately Regulus thought the Dark Lord seemed suspiciously casual regarding the search. It was almost like…but no. James and Lily had Sirius as their secret keeper. There was no way the Dark Lord had gotten any information from him. Yet. "Just be careful Siri." Turning, Regulus apparated back to Grimmauld Place.

September 23, 1981

"I-I think he knows Siri!" Regulus trembled as he clutched his brother's robes. "I think he k-knows that I'm s-spying!" Sirius pulled him closer, running a soothing hand over his back. "Don't go back then. You've done enough." Reg felt his chest ache at the gentle concern. "I have to, at least for one more meeting. He's going to name the date for the attack on the Longbottoms and Potters." He knew Sirius felt torn between his safety and his best friend's. He reached up and tugged a lock of Sirius' dark hair with a forced playfulness. "I'll be fine Siri. I've lasted this long." He let his head rest on his brother's chest for another moment. This could be the last chance he had to hug him. As if in confirmation of that thought, his mark began to burn painfully. Regulus pulled away. "I've got to go Sirius." He quickly tugged on the death eater robes he had brought and tugged up his sleeve. As soon as he touched the mark, he'd be taken inside the Dark Lord's wards. He took a last long look at his brother. "Bye Sirius." He brought his hand to the mark. At the last second a heavy weight latched onto him, before he was pulled away to Riddle Manor.

"Sirius!" Regulus looked over at his brother in shock. Sirius had managed to grab him as he disappeared and now both Blacks were in the middle of the Dark Lord's hideout. "What are you doing?!" He hissed, irate that his brother had followed him. Sirius grinned. "I'm not going to let you face the Dark Tosser by your lonesome." Regulus scowled. "You're mad! You'll get us both killed for sure!" Sirius shook his head. "Don't be so certain Reg." The older Black pulled his wand. "Love you Reg." One quick Petrificus Totalus later, Regulus Black was laying frozen on the floor, furious and terrified. Sirius stripped off his death eater robes (with a bit of difficulty due to his being petrified) and put them on with a grimace. Pulling a silvery item from some hidden pocket, Sirius draped it over him carefully. An invisibility cloak? Sirius grinned at him again. "It's James'. I borrowed it. Make sure to give it back." Sirius winked at him and donned the bone white mask. "See ya little brother."

Hours passed. Suddenly, the petrification on him was broken. Oh no! Sirius! Sweet Merlin no! Getting shakily to his feet, Reg adjusted the cloak and crept into the hallway. Voices approached him and he pressed himself into an alcove, listening hard. "Can' t believe Black went traitor. Just like that brother of his." Regulus recognized the speaker as Dolohov. "Yeah," McNair chimed in, "Who would've thought little Regulus would disobey mommy and the Dark Lord?" Regulus winced. "At least the traitor got his!" Reg felt the color drain from his face. Sirius! Suddenly the two came into view, dragging a bloody, mangled body behind them. Regulus wanted to puke.

"Avada Kedavra! Avada Kedavra!" Dolohov and McNair fell to the ground with a thump, never seeing their murderer's face. Regulus rushed over to Sirius, tears running down his cheeks. "Siri? Siri?" Reg mumbled over and over, clutching his brother's rapidly cooling body. Tears nearly blinding him, he hauled Sirius over his shoulder, not minding the blood that drenched him. "I'll get you outta here Siri. I promise." He wandered out of the mansion with his brother's body, by some miracle remaining unseen. "Now the apparition clearing isn't too far from here…" He kept up a running commentary, more than a little hysterical and most definitely in shock. He was so sure Sirius would pop back up with that devilish grin and answer back. Regulus let out a bitter sob. Sirius was never going to answer back. It was all his fault.

October 31, 1981

Regulus wandered up to the smoking remains of Lily and James Potter's cottage. Faintly he could hear a baby crying. Sirius' godson. Harvy? Haley? Harry? Yes Harry. Reg gingerly crept up the damaged staircase. The steps creaked ominously beneath his weight. A few more tense seconds and he was on the second floor. The crying was coming from a room to his right. Walking in, he saw a red haired woman lying motionless on the floor. A few feet away was a pile of black robes and ash. A small dark haired toddler stood in his crib, grasping the bars and wailing. Reg hesitated, then walked over to the woman first. No pulse. Gulping, he shook off his cloak and laid it over her as tenderly as he had covered James with a conjured sheet. Then he turned to the child.

Harry was staring at him with big green eyes, his wailing quieting to small sniffles. The toddler reached out, obviously wanting to be held. Unsure and awkward, Regulus reached into the crib and picked the child up. He winced as Harry snuggled close, wiping his mucus and tears all over. Ugh. Why do people want kids again? Ignoring his discomfort, he carefully carried Harry back downstairs and out of the house. Harry was Sirius' godson, and with Sirius and the Potter's dead Regulus had no idea who the child would go to next. Well he wouldn't let anyone else take his responsibility. Sirius had died for him. All of Siri's responsibilities were now his. With that thought firmly in mind. Regulus pulled up the hood of his cloak and made sure Harry was covered and warm. Humming softly to himself, he took one last look at the cottage and strolled gracefully down the street.