Isabelle drove the dagger home.
"Isabelle." He was gasping.
She paused for a moment, startled at the shape of her name on his lips, and then she switched Jace's hunting dagger to her right hand and pressed it against his throat. Blood spilled from a shallow gash. Isabelle tightened her grip at the sight of scarlet, wanting to spill more of his blood - all of it. But something in his expression stopped her.
His eyes were blazing. "Isabelle," he said again. "Not bad. Though I think your balance technique could do with a little training."
"SHUT UP! Shut up, you bastard! You killed Max - my little brother-"
"But not you." His eyes searched her face in wonderment. "I didn't kill you. I couldn't bring myself to do it. Looking at you, at those fathomless black eyes, so much like my own, I couldn't bring myself to do it. You reminded me too much of myself." He must have felt her shock, for a small smile played about his lovely mouth. "Isabelle Sophia Lightwood," he said, and Isabelle gasped on top of him.
"H-how do you know my name?"
"You have a ruthless heart in you," said Sebastian. His chest rose and fell steadily beneath her, his heart pounding deep into her bones. "You crave destruction. You are a fearless Shadowhunter - I have seen it, I saw it in your eyes in Alicante, seeking vengeance. You let it drive you, as do I. You want what you want when you want it, and nothing is this world can stop you from pursuing it. Battle lures Shadowhunters like moths to light." He was grinning. "Your father had an affair. How do you know your mother never knew of it and got her own back? Because she did."
She jerked back now, as if he'd pushed her. Her mind was whirling. For a moment Isabelle wondered if Sebastian was going to crack her across the face given the opportunity of her distraction, but instead he crossed his arms behind his head and looked up at her, his expression thoughtful.
"My father and your mother - they had an affair behind your father's back. You once asked me why I did it, why I killed your brother and spared you. But you already know the truth, Izzy. Max was just my little brother as he was yours. It was an accident. But you, Isabelle"- and he smiled, a wicked smile, as if he knew all the secrets in the world -"you are my sister."