"Detective Conan: Zero's Tea Time" is a spin-off manga series centered on Rei Furuya, a key character from the main "Detective Conan" series. Rei Furuya operates under three distinct identities: as a public safety officer, as an undercover agent within the Black Organization under the alias Bourbon, and as a part-time employee at Café Poirot under his civilian name. The narrative explores the complexities of his triple life, delving into his personal struggles, professional duties, and the moral ambiguities he faces.

The story unfolds through episodic chapters, each focusing on Rei's interactions with various characters from the "Detective Conan" universe, including his colleagues at the Public Security Bureau, his acquaintances at Café Poirot, and his adversaries within the Black Organization. The manga provides deeper insight into Rei's backstory, revealing his motivations, his loyalty to his country, and his internal conflicts as he navigates the dangerous world of espionage. Key moments include his interactions with Amuro Tooru, his alter ego at Café Poirot, and his tense encounters with members of the Black Organization, particularly Gin and Vermouth.

Rei's relationships with other characters are a central focus. His dynamic with Azusa Enomoto, his coworker at Café Poirot, highlights his ability to maintain a facade of normalcy despite his high-stakes undercover work. His interactions with Conan Edogawa and Kogoro Mouri occasionally intersect with the main series' events, adding layers of continuity. The manga also explores Rei's past, including his time at the police academy and his connection to a former classmate, Hiromitsu Morofushi, whose death profoundly impacts him.

The tone of the series balances action, intrigue, and moments of introspection, offering a nuanced portrayal of Rei Furuya. The narrative structure alternates between present-day events and flashbacks, providing context for his actions and decisions. Themes of loyalty, identity, and sacrifice are recurrent, as Rei grapples with the ethical dilemmas of his work and the personal cost of his undercover mission.

"Detective Conan: Zero's Tea Time" serves as a character-driven expansion of the "Detective Conan" universe, offering fans a deeper understanding of one of its most enigmatic figures. The series complements the main storyline while standing on its own as a compelling exploration of Rei Furuya's multifaceted life.