Haitatsu sarenai santsu no tegami (1979)

The Karasawa family are prominent in Hagi. Mitsumasa, who runs Nagato Bank, and his wife, Sumie, have three daughters: their eldest, Reiko; their second, Noriko; and their youngest, Keiko. One day, Robert “Bob” Fujikura, the grandson of Mitsumasa’s older sister Kimiyo, who lives in California, comes to visit. Bob has been studying East Asian history at a university in Chicago and has come to Japan, hoping to learn more about his grandmother’s homeland and relying on his great-uncle Mitsumasa for help. Noriko is engaged to Toshiyuki Fujimura, an employee of Nagato Bank. But ever since Toshiyuki suddenly disappeared three years ago, she has shut herself away in her room and lived as if her soul had left her. Then Toshiyuki suddenly turns up at the snack bar run by Reiko. When Noriko learns he has returned to Hagi, she is overjoyed, and her smile returns for the first time in a long while. Mitsumasa rebukes Toshiyuki for his dishonorable conduct, but Noriko says she still wants to marry him. They marry, three years later than planned, and leave for their honeymoon in Europe. After they return, the couple move into an outbuilding on the Karasawa property, but Toshiyuki’s younger sister, Tomoko Fujimura, shows up uninvited. Toshiyuki immediately tries to send her away, but Tomoko decides to stay, despite speaking sharply to everyone in the Karasawa family. A few days later, Noriko reads letters in three envelopes tucked among Toshiyuki’s books and looks stunned. Worried by her strange behavior, Keiko and Bob search for the letters while the family is out and discover what they say. All three are from Toshiyuki to Tomoko. The first, dated August 11, says that Toshiyuki’s wife will fall ill; the second, dated August 20, says that her condition will become critical; and the third, dated September 1, reports her death. Bob tells Keiko that it is strange that all the dates are in the future. Before long, Toshiyuki starts asking for money and trying to raise funds, and the relationship among Toshiyuki, Noriko, and Tomoko grows strained. Then, on the dates given in the letters, Noriko is poisoned with arsenic and vomits; immediately afterward, she takes an antidote herself. Mitsumasa does not report the incident to the police, but asks Prosecutor Minegishi to investigate it. On September 1, at Toshiyuki’s birthday party, Tomoko gets drunk and behaves obnoxiously toward Noriko. She takes Noriko’s glass and drinks from it. Noriko gets a fresh glass, drinks, and collapses. Shortly afterward, while Noriko is being tended to, Tomoko collapses and dies. From their conversation with Noriko, Prosecutor Minegishi and the police learn about the three letters. Arsenic is found in the glass Tomoko drank from, among other things, so the police take Toshiyuki, who prepared the drinks, in for questioning. He remains silent. Keiko and Bob travel to Kushiro, Hokkaido, where Toshiyuki stayed during the three years he was missing, and learn the truth about the relationship between Toshiyuki and Tomoko. Recalling how the party guests moved about, Bob begins to figure out who the culprit is.