S4.E8 ∙ The Client

A wealthy man purchases an old mansion but is perplexed to find a mysterious locked room.

The Tokyo Metropolitan Police Department's First Personnel Division is an elite group responsible for inspection work to uncover misconduct among the more than 40,000 personnel who work for the police force. It is said that just being the subject of an inspection can end a police officer's career. Feared as police of the police, inspectors like Sara Masaki have a lonely role. Two years on, Sara comes face to face with a conspiracy that will rock the entire police organization.

At the end of the year, a poison gas terror attack takes place at a terminal station in Tokyo. 666 people die or are injured in the attack.The terror attack's number of victims is related to the "number of the beast" and the case is given the name "The Beast." The person who carried out the attack is a 25-year-old popular actress, Kotone Kido, who died at the terminal station. Kotone Kido had a childhood friend named Hajime Kanzaki (Hiromitsu Kitayama). They were not blood-related, but they were very close like a brother and sister. Now, Hajime Kanzaki is 33-years-old and works as an undertaker. He wants to find out why his childhood friend committed the mass murder, who made her do that, and was there a chance she could have been stopped. While he investigates, he is killed by someone. At that time, he travels back in time and meets Kotone Kido again.

Yukihira Natsumi is a no-nonsense, intelligent Tokyo homicide cop known as the department's "number one" case closer who nevertheless also has a bad reputation for not working well with others and pushing the limits of the law. As she sees it, her only job is bringing in the bad guys and the results are all that counts. However, she is haunted by a hostage case five years prior in which she had to pull her weapon and kill a man, which earned the ire and distrust of some of her coworkers and members of the community. To bring balance to her life, Natsumi must find a way to deal with her demanding work, the aftermath of a divorce, and caring for her young daughter-all while chasing down a serial killer who's taunting the police with serialized short stories that foretell the next murder with no time to spare.