This story is actually two separate ones that are entwined yet parallel to each other. The first story is about Ruth who finds a well preserved bento box containing Nao's diary along with old letters and an antique watch. The narrative switches between Nao (a Japanese teenager who originally lived in the States but had to return to Japan) and Ruth's story.
Nao's narrative is compelling stream of consciousness. She's not in a good place mentally and physically. Neither is the world around her. She is tormented by her classmates and her home life is fraught with other issues.
Ruth almost doesn't read the diary or abandons it. Her part begins as the forensic portion of the tale. She gathers the superficial clues as well as the NOW. She is also our ticket to Nao's past. Eerily, as the narrative progresses, you see similarities between Ruth and Oliver with Nao's parents as well as certain aspects of Nao's life. But that thread is not nearly as compelling as Nao's story.
What kind of throws me is the last part of the book. I was very curious to see how she was going to handle the present as the past narrative was catching up to the NOW. While I did like having closure, I wasn't sure how I felt about the supernatural part of it. It just came out of nowhere for me or just too fantastic out of nowhere. I suppose it made things exciting but it didn't really work for me though I do get what she was trying to do. The other part is that while I'm glad about the outcome, I felt that the outcome came without the development we saw earlier and in some way felt like a tighty quick wrap up.
Truthfully, I don't know if the writer had a choice but to tie things up the way she did. We have dueling narratives and Nao's would have ended where it did. Anyhow, I also really enjoyed the very end and the continuity of it.