Naoko is a novel by Keigo Higashino. The original title is Himitsu (秘密, Secret). The novel won the 52nd Mystery Writers of Japan Award for Best Novel. The story centers on a man whose wife and daughter are in a terrible accident; the wife dies, but when the daughter wakes up, he discovers his wife's mind inside.
It was made into a 1999 Japanese film, Himitsu, directed by Yōjirō Takita. The 2007 film The Secret is based on the Japanese film.
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