Kazuto Ishikawa is a first-class architect. He is married to Kiyomi. They have a son, Tadashi, who attends high school and a daughter, Miyabi, who attends middle school. They live together in a refined home, designed by Kazuto. An injury causes Tadashi to quit playing soccer. Since that time, Tadashi often stays out all night without permission. One evening, Tadashi leaves home and does not return. Kazuto and Kiyomi become worried about their son and consider going to the police. News then reveals the murder of Tadashi's classmate. The police suspect that Tadashi might be involved in the murder.
Young public prosecutor Keiichiro Okino is assigned to the department of the Tokyo Public Prosecutors Office that deals with violent cases, where he will work with Takeshi Mogami, whom he admires. When a money lender is killed and it is suspected that someone from Mogami’s past is the perpetrator, the team prepares to do his best in order to prove the alleged criminal’s guilt.
Kae Horii moves into her new flat in an undisclosed area of Kyoto. While unpacking her belongings, she discovers a hidden compartment behind a inconspicuous mirror. In that compartment, Kae finds a notebook, that turns out to be a diary belonging to the previous tenant. Later that evening Kae starts to read the diary. The writer of the diary is Ibuki Mano, a young lady about to embark on her first year as an elementary school teacher. Ibuki is also in love with a man named Takashi, who may or may not hold similar feelings for Ibuki.
