**Chapter 1: A Slytherin Slip-Up**

The dimly lit common room of Ravenclaw was abuzz with the sound of laughter and hushed conversations. Millie, a fifth-year student, sat nestled in a corner, surrounded by her friends, engrossed in a heated game of Exploding Snap. Her bright blue eyes sparkled as she laid down a card, only to be met with a groan from her friends. Just as she was about to make a witty remark, a deep, smooth voice cut through the chatter. "Millie, I think you might want to take a look at your attire," Serious Black said, a mischievous glint in his eye. Millie's gaze drifted to the speaker, and she smiled, her heart skipping a beat. Serious, the brother of her boyfriend, Regulus Black, was known for his sharp wit and charming smile. Millie's eyes scanned her outfit, and her smile faltered as she felt a sense of unease. That's when she noticed it – a Slytherin tie, awkwardly knotted around her neck. Her eyes widened in horror as she reached up to touch the offending piece of fabric. She was a Ravenclaw, through and through. She had never, and would never, don a Slytherin tie. "Did I... did I switch houses overnight?" Serious asked, a chuckle escaping his lips. Millie's face burned with embarrassment as she frantically tried to make sense of the situation. Without a word, Millie leapt to her feet, her eyes scanning the room for a familiar face. "Regulus, we need to talk," she called out, her voice urgent. The game of Exploding Snap was abandoned, and her friends exchanged curious glances. Serious's eyes followed Millie as she hastily made her way out of the common room. He raised an eyebrow, intrigued by the sudden departure. As Millie burst through the doors, she spotted Regulus sitting in the library, surrounded by stacks of books. His dark hair was mussed, and his eyes were narrowed in concentration. Millie's heart swelled with affection, but her anxiety pushed her to hurry. "Regulus, we need to talk," she repeated, her voice more insistent this time. Regulus looked up, a question in his eyes, but before he could ask, Millie plopped down beside him, her Slytherin tie still proudly in place. "Millie, what's wrong?" Regulus asked, his brow furrowed with concern. Millie took a deep breath, her eyes locked on Regulus'. "I... I was just in the Ravenclaw common room, and Serious mentioned I'm wearing a Slytherin tie. I don't know how it got there or what it means." Regulus's expression changed from concern to curiosity. He reached out, his fingers gently brushing against the tie. "This is an old Slytherin tie, one that... well, it's complicated." Millie's eyes narrowed, her mind racing with possibilities. "What do you mean?" she asked, her voice barely above a whisper. Regulus's eyes seemed to cloud over, and for a moment, Millie thought she saw a flicker of something – fear, perhaps, or uncertainty. "We should talk about this somewhere more... private," Regulus said finally, his voice low and measured. Millie's curiosity was piqued, and she nodded, her heart pounding in anticipation of what was to come.