During the 1930s, a period of rampant shifts is reshaping Japan's societal structure. Mitsuko Hoshino is a prime example of such change, being the first female detective to ever exist in the country. Despite receiving back-handed compliments on a daily basis regarding her gender and profession, Mitsuko would not change her job for anything in the world and strives to be the best at the Ginza Detective Bureau.

At a cafe, Mitsuko meets a handsome young waiter named Saku Yoshida, who requests help to find the owner of a shoe he found. After handling the case, Mitsuko is shocked to find out that Saku has not only been cast off by his wealthy family, but the college student is also now employed by the bureau to be Mitsuko's assistant! While their relationship slowly blossoms, the duo is tasked with solving mysteries side by side in these ever-changing times.