The Devotion of suspect X by Keigo Higashino p 298.

The Swedish don't have a monopoly on dense, well written mysteries. Higashino has found fame in Japan, but this is the first that I have read by him. It starts with the murder -- and there is no "mystery" about who done it. However, the reader is made to sympathize with Yasuko, a victim who has tried to escape from her low-life leech of an ex-husband. Like the proverbial bad penny, he surfaces again finding her new place of employment and follows her home demanding to rejoin her family. He threatens not just her but her teen aged daughter. After a brief struggle, he is dead on the floor of her apartment and she is planning on turning herself in to the police when she receives an unexpected call from her next door neighbor. He is a middle-aged high school math teacher who frequents the diner she works at. He offers his help to fix the situation and prevent her from reporting the truth to the police. He is a deep thinker, passionate about math but a former classmate of his is a consultant for the police. This is a book that I did not want to end because of my sympathies for the characters. There is a surprise and the end, while unexpected is satisfying.