Detective Kyosuke Kozu's Murder Reasoning 5

Newspaper reporter Kenzo let a strange woman Emi took taxi while on the way home from a business trip. Later, when he stopped by his girlfriend Nobuko's house to give her souvenir, he noticed that the suitcase had been replaced by Emi's. A knife with blood wiped out came out of Emi's trunk. Nobuko's older brother Kyosuke is a university professor, but he is also a famous detective. The next day, Kyosuke made Kenzo follow Emi's elder sister, Yuri, who came to exchange the trunk. Emi and Yuri are daughters of the landowner Kayama family, but they were both children of their ex-wife. His second wife, Shizue, has Miyako, another kid. Emi had a bad time with Shizue and left home, and she had just returned for the first time in three years...