Gaeseok leads an ordinary office life - or at least, one that appears so on the surface. Behind that façade lies his obsessive effort to maintain “normalcy.” But all of it begins to unravel each night, when the thudding noises from the basement below his apartment disturb his sleep.

Deprived of rest and pushed into a state of raw nerves, Gaeseok finally makes a mistake at work. To him, “acting normal” is his only goal in life, and the pounding from below feels like a ticking time bomb threatening to shatter it all.

Driven to the edge, he confronts the source of the noise by going down to the semi-basement. There, after his heated complaint, a strange man emerges, oddly familiar in the way he addresses Gaeseok. Ignoring the accusations, the man calmly follows Gaeseok upstairs… and proceeds to bind his own ankle to Gaeseok’s window frame.

Now locked inside Gaeseok’s room, the man refuses to leave. What is his purpose? And what was the true cause of the relentless thudding from the basement?

Original Webtoon