"It was you, wasn't it?"
The question rings through the silence and the darkness.
"What do you mean?"
Bellatrix knows what he means, and Sirius knows she knows.
Still, he asks the question in a different way.
"You were the one that killed mother, weren't you?"
A pause.
"Are you upset?"
"No, but why? Why did you do it?"
"I heard what she was doing to you. I knew what she was doing to you. I had to make her stop."
Sirius closes his eyes at the memory of his mom hurting him. It was still painful.
"Aunt Walburga deserved to die."
Sirius opens his eyes. "Thank you."
"You're welcome," Bellatrix says softly.
This wouldn't last. Sirius knew that Bellatrix and he would be enemies again when they one-day escape from Azkaban.
But for now, he would be thankful for what she did.