A literary critic named Yajima is set to be released from prison when he's handed a book by another prisoner. The book seems to contain a simple code tucked away in its pages, written on Yajima's own manuscript paper. As Yuuki and Rie Kaishou both piece together the code, they start to find messages that point to Rinroku Kaishou visiting Yajima's wife on several different occasions.
Soon, Yajima thinks that his wife was cheating on him and abusing his children when they found out, so he plans to strangle her in her sleep when Rinroku shows up with his children, safe and sound.
Later, the prisoner from before who refers to himself simply as "The Novelist" confesses to Yuuki that he created the case because he wanted Yuuki to play a part in his next story.