It's the Showa era, and Mitsuko Hoshino, Japan's first woman detective, has only her assistant Saku to turn to when things get rough. But when Saku's older brother Hitoya returns to Japan with a case of amnesia, Saku is the one who needs help! All Hitoya has is a London train ticket and a poster of an elderly woman... Will these clues be enough to uncover the secrets of Saku's family?