Himitsu (秘密 means secret in Japanese, and is titled Naoko in the US release) is the book by Higashino Keigo (東野圭吾.)
The story starts with Heisuke(平介) the ordinary blue-colar worker in Tokyo, who one day loses everything when his wife dies in an car crash while his daughter is left in coma. Days later, when Monami(藻奈美), the daughter recovers from coma tells Heisuke that she is Naoko(直子) because the spirit has transfered from the wife to the daughter. When Heisuke eventually is convinced that it is Naoko’s spirit in Monami’s body, they both decide to keep it a secret.
I finished this book the moment I got it, even though I intended only to read a few pages but could not resist to continue. Higashino Keigo, the author has presented serveral themes in this book, including the main: how would a adult man with normal sexual desire deal with the situation when his wife’s soul is inside his daughter’s body (by the way, his daughter is about 11 years old, but this is “not a rated-R book.”) It is also a story about second chance: when you are no longer a middle-age house wife and you have the chance to start all over again, what would you do differently. Also in irony and part tragedy comes the question: how would you do if your husband is physically your father?
The story does have a surprise ending, in which I first thought was not a good ending, but later realized that it is the only way to give this tragedy a happy ending. I did not read the english version of the book, so I do not know the quality of the translation, but I do recommend this book. If you have a chance, read a few page and see if you like it or not.
By the way, this book was made into a movie couple years ago in Japan, and apparently some French film company bought the right to the scripts. But the movie is going to be in English since it stars David Duchovny and Lili Taylor (English speaking French film based on Japanese novel.)