Everything belongs to JKR, but she says it's okay to play in it.
To Rule Among the Damned by Araminta Malfoy Potter
Pansy Parkinson stormed down the hallway, knocking portraits of Parkinson ancestors off the hall as she went and, to be frank, enjoying their howls of rage. She was not, positively not pleased to have been called home from Hogwarts on a Hogsmeade weekend. Draco had promised to take buy her something expensive, Blaise had promised to buy her a drink at The Three Broomsticks, and Theodore had made mad promises with his eyes about what he'd do if she let him walk her back to the castle. Crabbe and Goyle had promised to stay far, far away.
"Mother," she spat as she entered the sitting room of Louisa Melliflua Parkinson, "what could possibly be so important that... Mother?"
Louise Parkinson was huddled on the floor in a sobbing heap. Her hair was a cloud of tangles--like Grangers, Pansy couldn't help thinking--and her robes were wrinkled and stained.
"Have you been drinking again?" Pansy asked quietly. She didn't wait for an answer, but moved to close the heavy velvet shades over the leaded glass windows.
Louisa choked and sniffed.
Pansy sighed. She levitated her mother onto the forbiddingly carved four-poster bed with a flick of her wrist, and drew the coverlet up. After handing Louisa a handkerchief, she reached for the cord to ring for a house-elf to bring tea.
"No!" Louisa managed through her tears.
"Shall I summon Father, then?" Pansy queried.
Immediately, Louisa shouted, "No!" and began to sob ever harder.
Pansy crawled into bed beside her mother and pushed the hair out of her mother's eyes. Her mother didn't smell like whiskey or wine, and she never cried otherwise. "Tell me, Mummy. You're scaring me."
Louisa blew her nose and took a deep breath. "I want you to pack your things, anything you want to take with you. We have to leave tonight, before your father--before Linus returns. He mustn't know you were here. You must be safe at Hogwarts by sundown, but oh, I couldn't bear for you never to see your room again. To never see you again."
"You're mad, what--" Pansy started to pull away.
"Wait." Louisa pinched her bony fingers around Pansy's arm. "Listen. I'm going to go into hiding, but you'll be safe at Hogwarts. I never meant for this to happen. I had to pretend to keep you safe, but he knows, they both know! Pansy, Linus has sheltered you all these years, but he knows." She rose and pulled Pansy with her to the vanity. "Look there. Do you look like me?"
Pansy considered her own jet-black hair and gray eyes. "I'm not a blonde, no, but we have the same mouth. Funny that you and father both had light hair and I..." She faltered, giving over for the first time to a reality she had never bothered to face, had never needed to face. No one would dare point out such an inconsistency to a family as prominent as hers.
Louisa put her mouth close to Pansy's ear and whispered, her voice catching: "Linus Parkinson is not your father. Your father is Thomas Riddle."