The bathroom.

"it's early in the night, I've got time" she told herself, setting off down the corridor to the prefect's bathroom. The heel of her shoes clicked on the floor as she walked, but no-one was around to see her. As she rounded the corner, she noticed the potions cupboard open, she slowly approached and saw professor snape restocking the shelves. "evening professor" she said, propping the sack against the wall. Snape turned around quickly. "miss granger?" he said in his usual monotonous tone. "what are you doing out at this hour?" "I was just dropping some rolls of parchment off at the owlery" Hermione replied, holding the bag up. Snape nodded and Hermione carried on her way.

She stopped outside the prefect's bathroom and stepped through the archway. It was a secret room hidden from the rest of the school behind a magic wall, and could only be accessed by prefects. She passed through the wall and dropped the sack by the bench. She noticed one of the house-elves stood by a barrel full of water. "hi Gribble" she said, walking over to the elf. "miss granger, a pleasure as always. what can I do for you?" he replied, smiling. "well, my clothes got quite dirty, would you be able to give them a quick wash?" she asked, grabbing a circular basket from the stack. "of course, just leave them with me" he replied. Hermione went over to one of the curtained cubicles and drew the curtain shut. She stripped out of her uniform, as well as her bra, panties and socks. She grabbed the bathrobe from the hook, tied it around her and stepped out. "there you go" she said, handing the basket to the elf. She slipped her shoes on and grabbed her bag. "do you not want to stay?" gribble asked. "got other things to do. I'll be back later" she said, leaving the bathroom. The elf shook his head and started washing the dust out of Hermione's clothes.

After a long walk across the castle, Hermione finally made it to the owlery. She gently knocked on the door and stepped inside. "hello?" she called. A man slowly rose from his bed and stumbled over to her. "ah, miss granger. you finally brought the parchment" he said, taking the sack from her with a delighted look on his face. "hi Bertie. sorry I was late, I fell asleep" she explained, making Bertie chuckle. "well, on you go" Hermione nodded and made her way back to the castle. As she got to the great hall entrance, she noticed that her robe was slipping open slightly. She retired it and headed back to the prefect's bathroom. Suddenly, a hand grabbed her robe, pulling it off her. She heard a small chuckle, followed by the sound of footsteps hurrying down the corridor. "blast" she hissed, covering herself with her hands. She looked around and dipped into the small section. "now what?" she asked herself. the halls were still empty but she didn't want to ask anyone for help. "McGonagall should still be awake at this hour, but the bathrooms aren't too far away"