Shitamachi Scam by Michael Pronko

After the suspicious deaths of a seventy-something woman and a student recluse, Detective Hiroshi tracks a gang of scammers. Hiroshi teams up with Detective Ishii from the women’s crime task force, and together, they search for who’s been ripping off retirees in shitamachi, the old part of Tokyo. With his personal life on hold (almost), Hiroshi finds out who’s behind the scams and who’s behind the scammers—and who will kill for more than the scams.