The Devotion of Suspect X (Detective Galileo, #1) opens Goodreads in a new tab

Yasuko lives a quiet life as a good mother to her only child. When her ex-husband appears at her door without warning one evening, her comfortable world is shattered. As Detective Kusanagi of the Tokyo Police tries to piece together the events of that night, he finds himself confronted by the most puzzling circumstances he has ever investigated. Nothing quite makes sense, and a brilliant mathematician neighbor holds the key.