Tatsumi Detective Agency, standing in a corner of a certain town, has a tea room where clients can ask for advice.

The head of the agency, Reiji, has a penchant for tea due to his late mother's influence, and solves many cases with the deductive reasoning skills he developed during his career as a police officer. A talented but cheating female staff member from her ex-husband, Reiji's best friend, a lawyer who does things at his own pace, and a novelist who works at the agency while interviewing Reiji...