Score: 8/10
This is probably one of the most controversial works of Keigo Higashino. There are two major points of controversy in the book. Firstly, the two main characters, Ryo and Yukiho, both had a terrible childhood. After they grow up, Yukiho desperately wants to live a wealthy and well-respected life. In order to achieve her target, she manipulates and ruins the lives of many others, with Ryo as her accomplice. Many readers, including myself, feel a sense of both pity and hatred towards Yukiho. Her acts are despicable and cannot be justified with her childhood experience. However, on the other hand, Keigo Higashino also shows us how she is constantly haunted by her past experience, that even after she has received everything she wanted, she is still unhappy and would probably never be happy. This is the biggest controversy of the story, but also the best part of the story, that Higashino shows us how a victim of fate has eventually turned into someone who inflicts pain on others.

Source: http://crystalfaith.pixnet.net/blog/post/28410933
Another major controversy revolves around the relationship between Ryo and Yukiho. In contrast to the previous controversy, which the author has revealed too many cruel details of how Yukiho’s personality is shaped, Higashino decides to leave the relationship between Ryo and Yukiho in an ambiguous state and gives very little psychological descriptions on what do the two characters think about their relationship. Ryo is clearly obsessed with Yukiho, but we do not know if it is only infatuation, or something deeper and sincerer than that. On the other hand, Yukiho seems to be manipulating Ryo for her own purpose. However, when the moment when Ryo died is also one of the rare moments that Yukiho expressed her sadness. Personally, I think there can be many interpretations of their relationship, and that sense of ambiguity has actually made the book even better.
Source: https://www.wukong.com/question/6469375494243483918/