A series of suspicious deaths, starting with that of her boyfriend Kawazu Masayuki, prompts mystery novelist Yuki Rikako to investigate. She discovers that all the victims were once passengers on the same cruise ship a year ago and involved in an accident that left one man dead. Rikako must find out what really happened during that outing before more casualties result.
Investigations on a mysterious woman Toko started when Sonoe, a teacher and Toko's fellow faculty member, was found dead as a result of what seemed to be an unfortunate accident. Eiki, an insurance investigator, and Takeshi, an ambitious police detective, find links between this case and the deaths of Toko's 3 fiances, and are determined to uncover the truth.