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.

In their most monstrous case yet, Conan and his friends dress up as famous monsters for a murder mystery game set on a creaky ghost ship. It's an evening of spooky fun--until a real murder interrupts the game. Then it's up to Jimmy Kudo to figure out which rubber mask hides the face of a killer! But there's more than one monster on the loose. Faced with evidence that the Men in Black have discovered their real identities, Conan and Anita have only one hope: find the deadly assassin Vermouth before she finds them. Can they unmask the Syndicate's top mistress of disguise?