When Harry Potter survived the Killing curse as a baby, nobody knew that so did his little sister Lizzie. Asleep in the other room, Voldemort did not know she existed and didn't find her. Severus Snape rescued the girl and raised her as his own; but she knew who she was. What happens when Lizzie and Harry meet?

He can't leave the room. Her room. And it's all the Order's fault. Confined to a small space with only the Mudblood for company, something's going to give. Maybe his sanity. Maybe not. "There," she spat. "Now your Blood's filthy too!" DM/HG. PostHBP.