Three murder cases take place in Tokyo. Numbers are left at the murder scenes, possibly hinting at where the next murder will take place. An investigation begins of the serial killer and Detective Nitta Kosuke works on the case. He believes the next murder will take place at Hotel Koruteshia Tokyo. To catch the killer, Kosuke goes undercover and begins working at the front desk of the hotel. <[>Yamagishi Naomi works at the front desk of Hotel Koruteshia Tokyo. She is selected to train Kosuke for his front desk job, but they can't get along. Kosuke is focused on catching the killer, but Naomi prioritizes the safety of the guests. As they begin to understand each other's differences, they also begin to build trust between each other. Who is the murderer?