In 1925 (year 14 of the Taisho era) baseball is still quite unknown in Japan and there are only a few male teams. After being told by a baseball player that women should become housewives instead of going to school, 14-year-old Akiko invites her friend Koume to start a baseball team in order to prove him wrong. During this time, when even running was considered too vulgar for women, baseball is known as what the boys do and they face many difficulties when having to find enough members, to get permission from their parents and also when learning about the sport itself, which they soon discover to be more difficult than expected.

Toys are powers bestowed upon those chosen to wield them, each having qualities that are unique to their users. Some of these individuals are born pure, using their powers to become detectives. Others bloom laced with poison and choose to become phantom thieves. These two opposing factions caused the formation of various detective academies around the globe—training detectives to fight and catch the phantom thieves. Sherlock Shellingford, Nero Yuzurizaki, Hercule Burton, and Cordelia Glauca form Milky Holmes, a group recognized as the cream of the crop in the Yokohama-based Holmes Detective Academy. However, in a skirmish against the phantom thief Arsene, their Toys suddenly disappear, deeming them unfit to continue as detectives. Stripped of their prestigious life and thrown into a rundown attic, they face expulsion if they fail to regain their powers within the next three months. Tantei Opera Milky Holmes tells the story of a once-legendary group in their journey to recover their Toys, as well as attempting to continue their line of work without the powers that once defined their career.

For high school student Tanaka, the act of being listless is a way of life. Known for his inattentiveness and ability to fall asleep anywhere, Tanaka prays that each day will be as uneventful as the last, seeking to preserve his lazy lifestyle however he can by avoiding situations that require him to exert himself. Along with his dependable friend Oota who helps him with tasks he is unable to accomplish, the lethargic teenager constantly deals with events that prevent him from experiencing the quiet and peaceful days he longs for.

Second season of Tantei Opera Milky Holmes.