Keiichiro Nagumo was once a legendary teen detective, his brilliant mind and youthful energy thrilling the nation as he solved impossible cases with flair. That was over a decade ago. Now, at 35, he runs a failing private detective agency from a rundown office, struggling to pay rent and living off a diet of sad, solitary tomatoes. His glory days are a distant memory, replaced by chronic back pain, crippling tooth sensitivity, a bewildered ignorance of modern technology like smartphones, and an inability to even order a coffee. Just as he resigns himself to a quiet decline, his life is upended by the sudden appearance of Mashiro Nakanishi, a relentlessly energetic high school girl who barges into his office demanding to be his assistant.

Mashiro is everything Nagumo is not. She is brash, physically superhuman, and possesses an uncanny ability to produce an endless arsenal of items from her school uniform, ranging from frying pans and stunt mats to fully loaded flamethrowers. While she claims to be a massive fan of his past work and is determined to restore him to his former greatness, she shows no hesitation in calling him out on his lecherous or outdated behavior, quickly establishing a chaotic and often absurd partnership. Reluctantly accepting her help, Nagumo finds his old-school methods of deduction clashing and, surprisingly, complementing Mashiro’s brute-force, modern approach to problem-solving. Together, this odd, generational-gap duo begins to take on the low-stakes, eclectic cases that come their way, from chasing lost cats that turn out to be the wrong cat, to clearing out wasp nests that accidentally lead to the decimation of a local yakuza office.

The series is set primarily in and around Nagumo’s shabby detective agency, likely in a district like Shinjuku, which becomes a hub for a growing cast of eccentric characters. Their first case introduces Cerberus, a stray calico cat kept as the agency’s reluctant mascot. After the mistaken-identity pet case, Mashiro’s dismantling of a yakuza den results in the recruitment of Taro Nezu, a timid former gangster who now lives in fear of Mashiro and serves as an errand boy. The duo is later challenged by Yuu Asunaro, a handsome and genuinely popular modern teen detective who idolizes Nagumo and seeks to become his apprentice, much to Mashiro’s chagrin. Accompanying Yuu is his beleaguered and hyper-competent assistant, Hana Kazamaki.

Early narrative arcs establish the series’ core comedic dynamic and introduce its recurring gags. One notable arc follows Nagumo and Mashiro going undercover as students at a college to investigate a case of abusive emails, where Nagumo’s attempts to use a secret cigarette code are comically ignored. Another significant thread involves the arrival of the Phantom Thief Beaver, the precocious young daughter of a police detective friend, who steals trinkets from the agency in an attempt to become Nagumo’s self-proclaimed arch-nemesis. Beneath the slapstick humor and bizarre cases, hints of a deeper backstory emerge, with suggestions that Mashiro’s devotion is rooted in a secret guilt for being the cause of Nagumo’s original downfall, adding an undercurrent of mystery to the relentless comedy.