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Advertising editor Zheng Yuting (played by Kim Ji-soo) was stabbed 9 times and died tragically in Room 1207 of Gangnam Hotel. The police captured a criminal suspect, Kim Yong-hun (played by Shin Ha-kyun), through surveillance video. At the time of the incident, he was hurriedly carrying a gasoline bottle and preparing to flee the scene. Police officer Choi Yeon-ki (Cha Seung-won) interrogated him, and the entire process became a reference video for the TV station's judicial debate. After that, the police began to collect extensive witness testimonies, including gas station employees, Japanese passengers in the elevator, hotel owners and waiters, blind masseurs, colleagues of the deceased, and even a magician... During the police investigation, they found that the deceased turned out to be the mistress of the father of a dancer (played by Park Jung-ah). As a result, they began to suspect that she and her boyfriend (played by Liu Chenglong) deliberately killed the mistress, but the interrogation ended in vain. In the end, when Officer Cui thought he was sure of victory and revealed the identity of the murderer, he discovered another truth...