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.

When Conan gets an invitation to London, he's thrilled. What could be better than visiting the home of his hero, Sherlock Holmes? But there's only one way he can get there: by becoming Jimmy Kudo again! Temporarily returned to his true age, Jimmy sets out on the trail of a devilish serial killer plotting an attack at the Wimbledon tournament. With London in turmoil, can Jimmy find a chance to confess his feelings to Rachel, or will love mean zero in tennis as well as well as in life?