Detective Conan, also known as Case Closed. At the beginning of the story, 17-year old (16 years in the manga) high school student Jimmy Kudo (Shin'ichi Kudo) becomes the boy, Conan Edogawa. Jimmy Kudo in the beginning of Case Closed is known as a high school student detective. One day, Jimmy goes to a theme park named "Tropical Land," with his childhood friend (or current girlfriend), Rachel Moore (Ran Mori). He encountered a case where a roller coaster passenger, Kishida (Kenneth in the English anime), is killed in a spectacularly bloody decapitation.He solved the case and on his return home, he witnesses a suspicious deal involving some men dressed completely in black. Another man in black spots him, knocks him down, and gives him an untested poison named Apotoxin-4869 (APTX4869), which is intended to kill him. The poison does not kill him. However, when he comes to his senses, his body had shrunk down to the size of an elementary school boy.
Detective Conan, following the advice of Dr. Hiroshi Agasa (Dr. Herschel Agasa in the English anime), Jimmy hides who he really is, lest the men in black find out that he is alive. When Rachel asks for his name, Jimmy spots books by Arthur Conan Doyle and Edogawa Rampo and comes up with the name "Conan Edogawa." Agasa says that "Conan" is a relative of his, but was too busy to take care of a young child, and suggests that "Conan" go live with Rachel, and both Conan and Rachel agree.
Rachel's father, Richard Moore (Kogoro Mori) is also a detective, but is not very capable. Conan always solves mysteries in his stead. As Conan appears to be just a boy, police don't pay Conan any mind. Conan instead uses Detective Moore by putting him to sleep with a "anesthesia gun-watch" and pretending to be Moore by using a voice changer disguised as a bow tie. Other important characters that appear (some later) are Jimmy's parents Booker (Yusaku) and Vivian (Yukiko) Kudo , Harley Hartwell (Heiji Hattori), a rival detective from Osaka, gentleman thief Phantom Thief Kid , who also appears in Magic Kaito), inventor of the APTX4869 Shiho Miyano (codename "Sherry" within the black syndicate, turned into a child also after she took her own drug to escape the organization, and then lives with Dr. Agasa under her new name Ai Haibara), and the other members of the black organization: Gin, Vodka, Tequila, Calvados, Pisco, Vermouth, Kir, Chianti, Koln, and a mysterious "boss" who has only been mentioned so far.
Detective Conan to maintain his cover, Conan goes to elementary school and has made particular friends with three children at the school, George Kaminski, Mitch Tennison and Amy Yeager who form the self styled Junior Detective League. Although Conan feels profoundly self conscious playing with them given his true age, the foursome have numerous adventures of their own and the normal trio have proved capable assistants to the detective for their age.