Famous Detective, Kudo Shinichi (Jimmy Kudo in English), gets turned into a child by a drug given to him by two suspicious looking men. Now in the body of Detective Conan Edogawa, he solves mysteries/crimes/et cetera with Richard Moore (I forget his name in Japanese) and his daughter, Ran (Rachael). He tries to find the men who did that to him to get back to his normal size, all the while dodging suspicion. Ran used to, at least, believe that he really was Jimmy.
Anyway, now that the explanation (the crappiest explanation ever) is over, there are 18 seasons and over 500 episodes. But don't let the size fool you (or my summary). It's all awesome.