"Summer's Secret" is a gripping film about the protagonist chihiroAfter hearing the news that his adoptive father, Gunji, was in critical condition, he returned to his hometown, a seaside town where he had been away for six years.ちひろ's adoptive father, Junji, was a policeman. On the day that his own daughter Miyuki was killed, chihiro was attacked by a mysterious person. The mysterious man forced Chihiro to take off her clothes, put a gun on her body, and suppressed her. After this incident, Junzhi resigned from his police job.
chihiro Confided her thoughts to Guangyi at the shooting range, and she told him that she was adopted into this family at the age of 11 as a substitute for her daughter who was killed at that age. At dusk, chihiro and Koichi meet at the beach, looking for the body of her late husband, who committed suicide for 100 million yen insurance. chihiro also meets Kunji's younger brother Kunio and his late husband Misa, both of whom are looking for the body. Chihiro and Koichi's relationship grows closer day by day and eventually the two fall in love.
At the same time, a corpse floated out of the water. Kunio was very excited, but he was shocked when he learned that it was a misunderstanding. On the other hand, Koichi's ex-girlfriend Kaoru was extremely jealous of Chihiro's relationship with Koichi, she went to see Junji, told him that Miyuki's murder was caused by Koichi, and revealed that Junzhi's life was running out. The angry Gunji visited Chihiro without knowing it...