Andromeda didn't want to get up that morning. The blankets felt warm, pulled around her, and she could still smell her sister – and her own scent – on it. There was a part of Andromeda – and not a small part, either – that was trying to convince her that what had happened last night had been some sort of hallucination, or a dream or nightmare brought on by the shock of going off to school.

But she could still feel the spots on her chest where Bellatrix had pinched, and there was a strange ache between her legs where she had rubbed too hard. Andromeda could not have imagined that.

She trembled slightly as she sat up and dressed, avoiding eye contact with the other girls in the dormitory. She felt as though they must know what had happened, and that they were probably already whispering about her. Stop it! she wanted to scream, though none of them had said a word. Stop it, stop it, stop it! We didn't do anything wrong!

Had they done something wrong? Andromeda asked herself as she slung her bag over her shoulder and trudged down to the Common Room. If so, what was wrong about it? If she and Bellatrix lay in the same bed at night and doing that was right – which she was quite sure it was – then why did this feel like this should be wrong? It wasn't much of a progression from lying together in bed, surely…

There were only a handful of students milling around the Common Room, which was fine by Andromeda. The less people she had to deal with, the less people could find out about her and Bellatrix, for she was sure that anyone who looked at her could tell.

Keeping her eyes trained on the ground just in front of her, she made her way quickly out of the Common Room and into the corridor, quite sure she remembered the way back up to the Great Hall. She hugged her bag a little tighter, and started off in what she thought was the right direction.

Within ten minutes, it became abundantly clear that it was not the right direction at all.

The dungeon corridors twisted and turned in a maze so confusing that Andromeda couldn't have remembered the path she had taken if she tried, and the whole place was just looking less and less familiar. Her heart sped with panic. What if she got lost down here? What if she never found her way out?

Don't be stupid, a voice that sounded quite a bit like Bellatrix said. If you didn't turn up for class, they'd send people out looking for you. They'd find you here, and you might look like a bit of an idiot for getting lost, but they would find you.

What if they didn't, though? The corridors were so confusing – how could anyone navigate them?

Logic was failing Andromeda, and she was rushing ever faster through the twists and turns of the corridors, as though by increasing the speed at which she travelled them, she would get out faster – never mind that she was only getting more and more lost.

Stop! Bellatrix's voice in her head commanded her, and Andromeda froze.

The silence of the school settled over her. Before, with the pounding of her feet on the floor and her heartbeat in her ear, she had not realized just how far she must be from anything and anyone. It felt like the entire weight of the school was on top of her, and she was being crushed into the ground by it.

Her hands started trembling involuntarily, and her throat constricted with emotion, tears spilling down her cheeks. It was dark, the few torches lining the walls doing little to brighten the place, and though Andromeda had never been claustrophobic before, she felt it now. She felt like she was in a tomb.

She stood as still as she could, straining her ears for some sound, anything to indicate that she was not entirely alone down here. These corridors had to lead somewhere, there must have been someone else down here.

And, to Andromeda's profound relief, there was. She heard – from a distance, but still close enough – a long, low, breathless moan.

She didn't think about who would be down here or why they would be moaning. She just started, as silently as she could so as not to drown out the noise, making her way down the corridor. The sound grew nearer and nearer, until, at last, Andromeda rounded a corner and saw the source.

She immediately regretted it.

Bellatrix was leaning against the wall. This would have been wonderful – Andromeda could think of no one she would rather have met down here than her sister, who would know how to get out and who wouldn't tease her for getting lost – except for what she was doing.

Bellatrix was on her knees – strange enough in of itself – in front of Rodolphus Lestrange. Andromeda immediately shrunk back into the shadows, hoping he hadn't seen her, and peered out around the corner to watch what was happening.

Rodolphus was clutching the wall, his clothing dishevelled and his eyes half closed, and Bellatrix had her face buried in his crotch.

Andromeda watched with confusion and disgust as Bellatrix's head moved back and forth. She – Andromeda – craned her neck to try to get a look at exactly what Bellatrix was doing.

Before she could, though, Rodolphus let out a pained moan and his body trembled. Andromeda jumped a little – he looked as though he was having a seizure – but Bellatrix just moaned in response, then moved back, pulling – Andromeda's face twisted in disgust – Rodolphus's penis out of her mouth.

"Oh, Bella," Rodolphus moaned, but Bellatrix was already standing up. "My turn, Rod," she told him, pushing him down to his knees. She flipped up her school skirt, and Rodolphus eagerly pulled her knickers off and buried his face between her legs.

Andromeda swallowed hard, face flushing as Bellatrix moaned and rocked her hips against Rodolphus's face. She felt something wet inside her knickers, and she shifted. It felt so much like when Bellatrix had touched her last night…

"Mm- ohh…" Bellatrix moaned. "Harder, Rod, harder- oh, just there…"

She pulled the buttons of her blouse open and moved both hands up to the bra she was wearing, and Andromeda could not stifle a small gasp as Bellatrix massaged her breasts through the fabric, pinching nipples so erect that Andromeda could see them even from the distance she was at.

The noise of the gasp wasn't much, but it was clearly enough. Bellatrix's eyes flew open, and they fell on Andromeda, standing there in plain view.

There was a second in which their eyes locked, then Bellatrix cried out wordlessly, and clear liquid gushed over Rodolphus's face.

Andromeda shrunk back, hiding around the corner as Rodolphus purred something in a low voice. "All over my shirt…" was all Andromeda could make you.

"I'm sorry, darling…" Bellatrix's voice was unnaturally sweet and light. "I couldn't help it… what you were doing just felt so good… Oh, here." Her voice abruptly went sharp, and Andromeda peeked out around the corner again to see Bellatrix draw her wand. "Scourgify. There, happy?"

Rodolphus nodded and stood up, pressing his lips against Bellatrix's.

"Good. Go on, then, Slughorn's going to be wondering where you are…"

Andromeda watched Rodolphus turn and head off in the opposite direction from the way Andromeda had come, and as soon as he was gone, Bellatrix marched over to Andromeda and grabbed her arm. "Did you follow us down here?" she demanded.

"No!" Andromeda cried, shocked by her sister's violent reaction. "I- I got lost!"

"I'm sure," sneered Bellatrix. "You got lost and you just so happened to walk in on me and Rodolphus."

"I did!" Andromeda's eyes filled with tears and her lip trembled. "I got lost down here and I heard someone and I followed the noise and it was you and Rodolphus–"

"Oh, shut up!" Bellatrix snapped. "I don't want to hear it. Come on." She gripped her sister's wrist and pulled her down a new corridor.

"Bella, please don't be angry with me," Andromeda said in a tiny voice.

Bellatrix stopped and turned around, the frustration draining from her expression.

"Oh Andi…" she muttered. "I'm not angry… you didn't know any better…" She leaned down and gave her sister a quick hug. "I'm sorry."

Andromeda was wary, but she hugged her back. "What were you and Rodolphus doing?" she asked, though she had a feeling she didn't really want to know, given how she hated the idea of them doing anything together.

Bellatrix was silent for a moment, then said, "I'll tell you what, Andi. We both need to get up to the Great Hall now, you need to get your timetable and then we have classes… but… sometime… I'll tell you what it was that we were doing." She paused briefly, looking at her little sister with a slight smirk playing on her lips. "I'll show you."