Yasuko Hanaoka, a recently divorced, single mother owns a restaurant and she has a regular customer, Tetsuya Ishigami, her next door neighbor, a tad reclusive but brilliant mathematics teacher. Buying lunches from Yasuko's restaurant is the brightest part of Tetsuya's day. Things take a sudden change when Yasuko's abusive ex-husband shows up one night to extort money from Yasuko but is killed by Yasuko and her daughter. Overhearing the commotion from his room and deducing that the ex husband has been killed, Tetsuya Ishigami offers his help to the mother and daughter. He not only disposes the body, but also plots the cover-up step-by-step. When the body turns up and is identified, Yasuko comes under suspicion. Detectives seeks the help of Professor Manabu Yukawa, a physicist, who seeing the case has nothing to do with physics, initially refuses to help. However, hearing that his genius classmate, Tetsuya Ishigami is the neighbor of the suspect, Manabu Yukawa changes his mind.
