Disclaimer: I'm not J.K. Rowling, so I don't own these characters. Frankly, she can keep Peter.
I wrote this before Deathly Hallows so consider this an alternate death for Peter. It just came into my mind one night and the plot bunny kept gnawing until I wrote it. I don't particularly like Peter, so Peter fans (if any exist) be warned.
Peter Pettigrew entered Snape's home to find it empty. Well, almost empty.
"Bella, nice to see you," Peter stuttered. He was still afraid of her from when he was in school. She had been a seventh year and him a lowly first year but she had scared him with just a look.
Bellatrix grinned, licking her lips. She rose from her seat and now stood in front of a rather frightened Peter Pettigrew. "Hello, Peter, I can say it's nice to see you," she said as she walked around him like a hawk circling its prey. "I guess you haven't really heard that much in your lifetime, hm?"
Peter shook his head, words escaping him as Bellatrix stopped in front of him and her dress showed a good amount of cleavage. She smiled again as she twirled her wand. Soon, she stopped twirling her wand and pointed it at him with a wicked grin. "Aveda Kedevra."
Peter had no time to react his eyes shone with a green light as he fell to the ground, his silver arm twitching on its own. Bellatrix licked her lips as she kicked the body with her heel. "Good riddance to bad rubbish," she used a spell that sent the body out the door. She followed. "Incendio."
Peter Pettigrew's body went up in flames the night he died and no one knew or cared.