"Boys Detective" is a manga series centered around a group of young detectives who solve mysteries in their small town. The protagonist, Kaito Arima, is a high school student with a sharp intellect and a natural talent for deduction. Alongside him are his childhood friends, Rina Takahashi, who possesses a keen eye for detail, and Haruto Nakamura, whose technical skills and resourcefulness prove invaluable. The trio operates as an unofficial detective agency, taking on cases ranging from petty thefts to more complex crimes that baffle the local police.

The narrative unfolds through episodic cases, each presenting a unique mystery that challenges the protagonists' abilities. Kaito often takes the lead, piecing together clues with logical reasoning, while Rina provides emotional insight and interpersonal connections that aid in solving cases. Haruto's technical expertise, including hacking and gadgetry, often uncovers critical evidence. The dynamic between the three characters is a key element, balancing camaraderie and occasional conflict as they navigate the pressures of their investigations.

As the series progresses, an overarching plot emerges involving a shadowy organization tied to several of the cases. This organization, known only as "The Syndicate," becomes a recurring antagonist, with its motives and operations gradually revealed. The detectives' encounters with The Syndicate escalate in complexity, forcing them to confront personal stakes and moral dilemmas. The series explores themes of justice, trust, and the consequences of pursuing truth in a world where not everything is as it seems.

The setting is a modern-day Japanese town, depicted with a mix of everyday realism and heightened drama to suit the mystery genre. The art style emphasizes expressive character designs and detailed backgrounds, enhancing the atmosphere of suspense. While the series primarily focuses on solving mysteries, it also delves into the personal lives of the main characters, revealing their backstories and motivations. This blend of episodic storytelling and serialized plotlines creates a balance between standalone cases and long-term narrative development.