Severus didn't panic. He cast Protego, the dome catching the knockback jinx cleanly, and fired a disarming spell at the woman in the same motion. She blocked it without effort and stepped aside with a sharpness that meant she'd been in real fights before. She looked ready to follow up, but Regulus moved between them.
"Cousin, stop! He helped me!"
The woman gave Regulus a look of pronounced displeasure, pushed a strand of dark hair back from her face, and shifted her attention to Severus. Up close she was striking in the way the Black family often was: sharp-featured, aristocratic, with something predatory running just beneath the surface, like a blade kept inside a very fine scabbard.
"Grandmother has told you a hundred times not to go out alone, and not to associate with any Muggle-borns."
"I needed to pick something up," Regulus said, with the tone of someone who'd had this conversation before and had no energy left for it. "I wasn't expecting a trap, or to be used as a kidnapping target. I wanted to handle it myself. I'm sorry."
"I see." Bellatrix's eyes moved back to Severus, still hostile. "I'm not thanking you. What do you want?"
He'd had an idea a moment ago, something to do with the Blacks and finding a Parselmouth. Then he'd seen the marks on her arm, and he'd put it away. He wasn't going to use that route.
"I'll keep it to myself."
"Tell me," Bellatrix said, voice hardening. "I don't want it known that the Blacks owe anything to a half-blood."
"Very well." Severus walked past Regulus and stopped in front of her. He smiled and let his gaze move unhurriedly over her face: the aristocratic pallor, the full mouth, the thick dark lashes, the eyes narrowed as she pressed her wand tip to his chest and held herself back, just barely, on account of the fact that he'd just saved her cousin.
"Then what I want from Miss Black," Severus said quietly, "is one kiss. A fair price for saving Regulus's life, I'd have thought."
"Would you like to die?" She said it with complete calm. The sparks moving in her eyes were not decorative.
"I was under the impression the Blacks never went back on their word."
Her eye twitched. The wand tip flared brighter.
Regulus had broken into a cold sweat. The tension in the alley was thick enough to press against your skin. He knew Bellatrix better than most, knew her absolute contempt for anyone who wasn't pure-blood, and knew her temper, and the particular pleasure she took in certain spells. The fact that she had not already shouted Crucio was a small miracle, and he was very aware that the miracle had an expiry date.
"You might want to reconsider," Bellatrix said, flat and dangerous.
"Of course not. It's not every day you meet someone as attractive as you."
Pure revulsion crossed her face, and the wand brightened again.
"Last chance. Ask for something else."
"All right, then I want nothing," Severus said, with a dismissive wave. "I shouldn't have expected anything different from pure-blood wizards. All talk and no follow-through. The only thing you're any good at is stabbing people in the back."
He walked past her, toward the alley exit, and didn't look back.
"You." Bellatrix hissed at his retreating figure. "You dare speak about pure-blood wizards like that, you filthy little Muggle-born. I will kill you where you stand."
She raised her wand at his back and couldn't bring herself to fire.
His words were still there, ringing, and if she struck him from behind right now, she would have just proved him right.
She ground her teeth, strode forward, grabbed his shirt, and shoved him hard into the wall. The wandtip pressed to his chest. Her other hand seized his collar, and she bit down on his mouth, sharp and furious.
How straightforward she is, Severus thought, with a private amusement he didn't let reach his face. But she needs to understand this isn't how it works.
He slid one hand to her waist, the other to the back of her head, turned her smoothly, and pressed her back against the brick. Bellatrix went rigid: a heartbeat of pure shock, anger surging behind it, and then a second, different shock as Severus kissed her back with a calm, unhurried confidence that had no right to exist given the circumstances.
It didn't last long. She came back to herself, bit his tongue hard, and he stepped back, letting her pull free.
"Lovely," Severus said, running his tongue across his lips. "Have you ever had strawberry cake before?"
A faint colour rose in her pale face, and whatever had been burning in her eyes went several degrees past anger into something more dangerous.
"I AM GOING TO TORTURE YOU, YOU ABSOLUTE BASTARD! CRUCIO!"
Severus stepped aside.
"CRUCIO!"
He stepped aside again. A black needle slipped from his pocket, unfolded in midair, and locked itself into a cube.
"CRUCIO!"
This time he didn't bother to dodge. He simply kept backing away, and the curse hit the cube and went nowhere. It flared azure and swallowed the beam entirely.
"CRUCIO —"
"BELLATRIX, ENOUGH!" Regulus caught her wrist as people began gathering at the mouth of the alley. Severus turned once, blew her a kiss, and disappeared around the corner.
"Let go of me! I'll kill him!"
"He's gone," Regulus said, straining to keep his voice down. "And if you keep casting in a public alley you're going to bring every Auror in the city."
Bellatrix tore her arm free, stared at the corner where Severus had vanished, then turned her cold gaze on Regulus.
"If you tell anyone about this, I will kill you."
"Of course," Regulus agreed, with a smile that cost him considerable effort, and silently cursed Severus from the bottom of his heart for leaving him alone with her.
Severus was fighting down genuine laughter as he walked back into Diagon Alley.
You're extraordinary, you mad woman. If Regulus hadn't been there you'd have tried to kill me before I'd finished the first sentence. But all the same.
He ran his tongue over his lip and glanced back at the unremarkable building that was the Leaky Cauldron. That was actually pleasant. It's been a long time since I've been interested in anyone.
He nicked his index finger and traced a small diamond on his palm in blood. After a few seconds it flared, contracted, and settled into a tiny tattoo: two centimetres square. He fed it a thread of magic, and an image of Bellatrix surfaced at once in his mind. She was currently destroying her room.
Getting anywhere with someone like that will be a serious undertaking. And Crucio does lasting damage to the mind: she's had it used on her more than once, and no simple restorative potion is going to cover that. Something to think about later. For now, at least he had a first-hand view of what was happening in the country.
The mechanics of what he'd done were straightforward: blood magic, operating on a simple principle. Bellatrix had bitten his lip hard enough to draw blood, and one drop was all the spell needed. If the target consumes even a trace of the caster's blood, the caster can form a seal within them and observe: health, mental state, whatever's happening in their immediate environment.
Right. Home. The potion isn't going to brew itself.
He looked toward the road and, with obvious reluctance, pulled out his wand and waved it.
The purple bus appeared. The door opened. The driver leaned out, beaming.
"Back already! Hot chocolate? A hot water bottle? Toothbrush?" The old man's enthusiasm was frankly inhuman.
"No."
"As you like!"
A few minutes later the bus braked hard, throwing Severus forward with what felt like personal malice.
//===================//