Ranko Ando (Karina) is a detective. She is 32-years-old and single. Ranko Ando does her job well and has solved difficult cases. She doesn't listen to others and doesn't care what others think about her. She works with detective Toshio Aoyama (Shigeaki Kato). He holds a strong sense of justice and cares what others think about him.
Sharaku Homonji (Yuji Oda) is the eldest son of a distinguished family who has studied crime for generations. The eldest son from the Homonji family has tested for an IQ of 246 for generations and Sharaku Homonji possess an IQ of 246.
Soko Wato (Tao Tsuchiya) is a detective. One day, she is assigned to the investigation section #1. Her job there is not to investigate crimes, but to escort Sharaku.
Detective Keita Kurokouchi (Tomoya Nagase) continues to extort money from politicians whom Keita Kurokouchi has information on. By using his information he is able to crack unsolved cases. Rookie Detective Mayo Seike (Ayame Gouriki) is excellent with her job and also a bit naive. She conducts an internal investigation on Detective Keita Kurokouchi, but they become partners and work on cases together.
Kazuko Yamase (Aoi Morikawa) is a 23-year-old, broken-hearted freeter. One day, she sees a knitted teddy bear that really appeals to her. She decides to buy it. Later, the knitted teddy bear suddenly speaks! Within the teddy bear, Yasuo Amano's (Sho Aikawa) spirit lives. He is the person who knitted the teddy bear and he was also detective. Kazuko then becomes involved in a case with Yasuo and helps to solve the case.
Rena Sasaki (Keiko Kitagawa) is a beautiful woman with excellent memory and intelligence. She becomes a private detective and risks her life to chase down evil private detectives, because her younger sister was murdered by a stalker. The person that provided information to the stalker on her sister's location was a private detective.
Shinobu Satomi (Tori Matsuzaka) works in the Mobile Investigation Unit of The Tokyo Metropolitan Police Department. The Mobile Investigation Unit conducts the initial investigation at all crime scenes. He works with Yuki Inokuma (Fumino Kimura). They are a couple, but they keep their relationship a secret at work. They both hope to work at the #1 Investigation Station. One day, they meet beautiful Kara Tachibana at the site where a dead body was found. Kara Tachibana appears at the other crime scenes involving grotesque murders. She shows an interest in Yuki Inokuma. Shinobu Satomi thinks it's a bad sign for Yuki Inouma. To protect his girlfriend from danger, he struggles to find uncover the truth behind the serial murder cases and Kara Tachibana’s identity.
Haruya (Yuta Tamamori) is a university student. He is smart, brave and curious. Haruya then becomes involved in a case and investigates like a private detective. Since then, Haruya works like a private detective to solve cases.