"Eiga Oshiri Tantei: Curry Naru Jiken" is a feature-length anime film based on the popular children's book series "Oshiri Tantei" (Butt Detective). The story revolves around the titular character, Oshiri Tantei, a detective with a literal butt for a face, who solves mysteries with his assistant, Brown, a talking dog. The film centers on a peculiar case involving a mysterious curry that causes anyone who eats it to lose their sense of taste.

The narrative begins when a renowned curry chef, Dr. Curry, creates a new recipe that becomes an instant sensation. However, shortly after its release, people across the city begin reporting that they can no longer taste anything after consuming the curry. Oshiri Tantei and Brown are called in to investigate the strange phenomenon. As they delve deeper, they uncover a plot orchestrated by a shadowy figure who aims to monopolize the culinary world by eliminating competition through the cursed curry.

Throughout the investigation, Oshiri Tantei employs his signature deductive methods, often involving humorous and unconventional tactics. The duo encounters various suspects, including rival chefs, food critics, and even a mysterious spice merchant. The story is filled with lighthearted moments, slapstick humor, and clever twists, staying true to the whimsical tone of the original series. The film also introduces new characters, such as Dr. Curry's apprentice, who plays a pivotal role in unraveling the mystery.

The climax reveals that the cursed curry was laced with a rare, tasteless spice designed to numb taste buds. Oshiri Tantei and Brown manage to track down the mastermind behind the scheme, leading to a dramatic confrontation. Using his quick thinking and unique abilities, Oshiri Tantei devises a plan to reverse the effects of the spice, restoring everyone's sense of taste and saving the culinary world from chaos.

The film maintains a family-friendly atmosphere, blending mystery-solving with comedic elements and a touch of adventure. It stays faithful to the source material, offering a straightforward yet engaging narrative that appeals to its target audience of young children while providing enough charm to entertain viewers of all ages. The story emphasizes teamwork, problem-solving, and the importance of perseverance, all wrapped in a quirky and entertaining package.