Jimmy Kudo, the son of a world-renowned mystery writer, is a high school detective who has cracked the most baffling of cases. One day while on a date with his childhood friend Rachel Moore, Jimmy observes a pair of men in black involved in some shady business. The men capture Jimmy and give him a poisonous substance to rub out their witness. But instead of killing him, it turns him into a little kid! Jimmy takes on the pseudonym Conan Edogawa and continues to solve all the difficult cases that come his way. All the while, he's looking for the men in black and the mysterious organization they're with in order to find a cure for his miniature malady.

While Conan tries to prove that a corpse found deep in the woods was the victim of more than just a hunting accident, the Junior Detective League gains a new member: a curious bear cub! Then Detective Moore's office is graced by a very traditional lady with very traditional--and very deadly--sword skills. And at a place called Mermaid Island, a woman is found hanged under a waterfall. It seems the legendary mermaid's curse has struck again...unless Conan and Harley Hartwell can find an all-too-human culprit!