the_debt_of_time

"I'm sorry, Sirius," Narcissa said regretfully.
"So am I, cousin." Sirius stared up into her terrified face. "Invocato Vita Debitum!"
Narcissa's eyes widened dramatically, and she stumbled as though someone was
pressing down on her shoulders, attempting to force her to kneel. "What are you doing?"
"You owe me a life debt, and I will call it in now with or without your consent," he
threatened.
Her voice broke as she whispered, "Sirius.. ."
"What's he talking about?" Draco demanded.
Sirius gave her a dangerous look that said he was at the end of what little patience
he had.
"Let him go," Narcissa ordered her son quickly. Draco pulled out his wand and set
loose the bindings that trapped Sirius. "Cousin, please, can you save us?"
Sirius stood up, shook off the ropes, and moved to the door. "Stay here," he ordered
them both, and then shifted back into his Animagus form. He was still unarmed, and
despite his power, he was no match against Bellatrix without his wand.
Silently slipping back into the drawing room, Padfoot flinched at the smell of blood
invading his nostrils, and his eyes widened as he saw Hermione lying on the ground, tears
streaming from her eyes, her arm extended and marred by the familiar scars carved into
her otherwise perfect flesh.
No, he thought. Not this. Not here. Not now.
Fury fuelled him as he crept forward in a silent frenzy. At the last second, he let out
a soft growl and watched as Bellatrix turned to see his dark frame. Padfoot launched
himself forward, landing on her body, pinning it to the ground, and knocking her wand
from her hand. She actually looked afraid for a split second, and he imagined how
wonderful it would feel to watch the bitch get carted off to Azkaban again. But then
Remus's words to Harry months earlier echoed in his mind:
"Harry, the time for disarming is past!"
And so was the time for mercy.
One glance to the side where Hermione's still body was sprawled on the floor sent
him teetering over the edge. He turned and bared his sharp teeth at his cousin, opening his
jaws wide enough to sink his wicked fangs into the flesh of her neck.