The Koishi Detective Agency

The page-turning Japanese mystery nominated for the 2026 Booksellers’ Award, perfect for fans of We Solve Murders and Mrs Shim is a Killer.

Welcome to The Koishi Detective Agency. Tucked down a side street in Fukuoka with furniture falling apart and power cables snaking the floor, work Private Detective Koishi and her team of two: Renjo, her rule-abiding sidekick and fellow investigator, and Hinami, the office assistant with her head in the clouds.

Koishi is fed up. She’s unintentionally made a name for herself solving infidelity cases when truthfully she couldn’t care less about love. What she wants are real crimes. She dreams of serial killers and locked room murders, missing murder weapons and deserted islands, anything but another scorned wife sobbing in her office.

So Koishi doesn’t hide her dismay when high school student Mio Sato shows up asking the team to investigate her father’s affair. But when Koishi and Renjo start to follow Mr Sato around the city, things are not as they seem…

The Koishi Detective Agency is a plot-driven upmarket/commercial novel that’s already sold 82,000 copies since publication in Japan in October. Set against the vibrant city of Fukuoka, it’s got the zippy dialogue of a Brooklyn 99 episode and a twist you won’t see coming.