"Tantei Opera Milky Holmes: Psycho no Aisatsu" is a short anime series that serves as a spin-off of the main "Tantei Opera Milky Holmes" franchise. The story revolves around the four members of the Milky Holmes detective team—Sherlock Shellingford, Nero Yuzurizaki, Elly Cunningham, and Cordelia Glauca—who are known for their eccentric personalities and unique abilities. These abilities, referred to as "Toys," grant them special powers essential for solving mysteries. However, in this installment, the focus shifts from their detective work to a more comedic and surreal narrative.

The plot begins with the Milky Holmes team receiving a mysterious letter titled "Psycho no Aisatsu," which translates to "Psycho's Greeting." The letter contains cryptic instructions that lead the girls into a series of bizarre and absurd situations. As they attempt to decipher the message, they encounter strange characters and surreal events that challenge their perception of reality. The narrative unfolds in a non-linear fashion, blending humor, absurdity, and occasional moments of introspection.

Throughout the series, the characters' interactions and reactions to the increasingly odd circumstances highlight their distinct personalities. Sherlock, the self-proclaimed leader, often takes charge but is prone to overconfidence. Nero, the energetic and impulsive member, adds a layer of chaos to their endeavors. Elly, the calm and collected one, provides a counterbalance to the group's antics, while Cordelia, the food-obsessed member, often serves as comic relief. The dynamic between the four remains central to the story, even as the plot veers into surreal territory.

The series maintains a lighthearted tone, with each episode presenting a new, self-contained scenario that contributes to the overarching mystery of the "Psycho no Aisatsu" letter. The narrative does not aim for a conventional resolution but instead embraces its absurdity, leaving viewers with an open-ended and whimsical conclusion. The focus on humor and character-driven moments distinguishes it from the more mystery-oriented main series, offering a fresh take on the Milky Holmes universe.