We have an attic that nobody uses. I hear knocks coming from it at night.

I have a storage room, right at the back of my house. It has a small wooden, box-shaped door in the ceiling, and it has always been there. My dad's office is also right infront of the storage room, you have to go through his office to get to it. Otherwise, you can go through the back garden to get straight to the storage room. My room is across the entire house, right at the front. My mother has always told me and my sister that we are to never touch, open, or go near the attic at night. That's why they lock my dads office, the door from the backyard to get into it, and the backyard itself. Whenever I used to ask about it whilst we were eating lunch, they would either ignore me or say that "it's for my own good". Me and my sister have always been curious about it. One night, as usual, my mother put me to bed, reminding me of our rule. I shortly after fell fast asleep, but only to wake up later during the night. I don't remember the exact time, but it was somewhere around 2am when I heard footsteps. They sounded as if they were coming from my dad's office, and approaching my room. I thought it was my dad, coming to check up on me to make sure Im asleep, as he always does, but I couldn't understand why they were coming from his office instead of my parents bedroom. Regardless, I shut my eyes and pretended to be asleep. I could still hear the footsteps. But they didn't sound like my dad's, I knew exactly what everyone's footsteps sounded like in the house. But other than my dad, no one else could've been awake. My sister and mother are both very deep sleepers, my dad's the only one ever to get up during the night. But the footsteps sounded thicker and deeper, they weren't my dad's. I shut my eyes immediately, pretending to be asleep. They got louder and louder until I heard them stop just at my bedroom door, but when I opened my eyes, there was nothing there. Knowing there was no one else I could talk to about it, I ran to my sisters room, just across from mine, and closed the door behind me. "Sis? You awake?" I whispered. "Yeah." She whispered back. She looked pale, a bit like a ghost. I sat next to her on the bed. "Did you hear that? Those footsteps." I explained. "Yeah. I did. They're new." She said back. "Do you think they came from the attic?" I whispered low, our parents hated when we spoke about the attic, especially late at night. "Only one way to find out." Shes gulped, getting up. "But, what about the locks? And besides that, it's dangerous. You know-" "I know where mum and dad keep the keys. Theyre not very good hidersa you don't have to come if you don't want to."Shes cut me off shorto creaking open the door to peak outside. I gulped and followed her with hesitation. Our parents had hidden the keys just underneath a side table in the hallway. My sister nelt down and picked them up, and then we crept to my dad's office. I could sense something was wrong the minute my dad's office was open. The smell was different. The vibe felt off. "Are you sure we should do this?" I asked. She just nodded. I stood back at the entrance of the office whilst she finally opened the storage room door. It felt as if something had been released. My sister shrieked in horror, but she was just, frozen there. My parents came running in, furious, but also worried. I couldn't see much, but I could see the attic door, open. Red dripping down from it. My parents dragged me away and shut the office door tightly shut. My sister screamed again, then it went dead silent. My parents and I stood there for 10 minutes, maybe even longer. Then, they told me to just go back to bed. To forget about all of it. But I couldn't. "Dad, is my sister going to be okay? What just happened."My questions to him flooded in and he just shook his head the entire time, whilst leading me and my mum back to our beds. The next morning I woke up to police, my parents, and my sister gone. No trace, no nothing. Just gone. Ever since then, I haven't even touched the storage room, and my sister, hasn't appeared anywhere either.