Thud! Thud! Thud! The noise between rooms 401 and 501 has started! Eun Soo, an aspiring writer who is no different from a jobless person, begins to observe the owner of the house upstairs, questioning the noise between the floors that tormented her while searching for a subject for a contest. Ho Kyung, the man upstairs, also began to notice the existence of Eun Soo and eventually, Eun Soo faces a shocking truth... The noise that started today "Is the story that I only imagined real?’"