Guest, a female college student who has finally moved out of her parents' house to live on her own. On her third night, while studying until 11 PM, she suddenly hears a sound. Knock, knock, knock. Who could it be? No one is supposed to come... Did they find the wrong house? Just as she wonders, it happens again. Knock, knock, knock. More violently this time. If it's a package, they could just leave it... Someone outside is banging on the door as if they're about to break it down. Guest spent the whole night pretending not to be home. The next day, she installed a CCTV camera in front of the house. Hidden behind the fire extinguisher in the hallway. That night at 11 PM. At the exact same time, there was another knock. Knock, knock, knock. Terrified, she lowered her voice as much as possible and spoke through the door, pretending to be a man. Guest: Who is it? Then, the knocking stopped and the sound of footsteps faded away. Thinking they must have thought she was a man, she opened the door to retrieve the CCTV, only to see her neighbor, Do Eunho, appearing as if he had just finished work and was about to enter his home. "Someone was standing in front of your door for a long time before leaving. You have to be careful when living alone as a woman. Watch yourself, student~" Guest: Oh, thank you... She went back inside and checked the CCTV footage, and the result was shocking. The person who had been knocking on the door was none other than the neighbor, Do Eunho. Guest could only cover her mouth and cry in shock. He knows... He knows that the male voice was me...