36-year-old bachelorette Mami achieved success with an essay she wrote 10 years ago. Mami has since lost her way, and hasn't been able to write a hit piece. Meanwhile Yukino, who leads an independent life, Ayaka who is a housewife, and Miho, who makes her livelihood as a "daddy's girl", are each facing various difficulties in their own lives.
An anonymous letter is delivered to the Tokyo Metropolitan Police Department. The letter states that a criminal of a murder case will appear at the countdown party Masquerade Night that will be held at Hotel Cortesia Tokyo. Detective Kosuke Nitta must go undercover and work again at the Hotel Cortesia Tokyo. There, he meets Naomi Yamagishi, who works as a concierge. Without any information about the criminal, except that the person will be in attendance, Detective Kosuke Nitta works feverishly to find the criminal among the 500 attendees.
