In a world of suspense and the supernatural, the famous detective Kudo Sute is attacked by mysterious men in black on his way home. After a fierce struggle, he tumbles down a hill and passes out. When he wakes, the men in black are still searching for him. He hides in a small house, where he finds an X pill on the table. Taking it will turn him into an elementary school student, and he can return to normal with an antidote. To evade capture, he takes the pill and changes his name to Edogawa Kaisen.
After enrolling in elementary school, Kaisen meets a group of children who have formed a young detectives' club. He joins in as if it's all a game, but in reality, the 24-year-old far surpasses the children with his knowledge and intelligence. His fellow Detective Conan character Professor Agasa is friends with Professor Yak. The professors' inventions, such as a launcher and a voice changer, help him solve cases. He sometimes stays at Professor Yak's house, but spends more time at Tingting's home. He also helps make a name for Tingting's father's detective agency.
He encounters cases involving Kaito Kid and Detective Conan, each full of challenges and suspense. Every time a murder occurs, Kaisen uses his keen insight and deductive skills to catch the real culprit, such as when Yakesi awakens after falling asleep.
The young detectives' club has two girls, a chubby boy, a thin boy, and Kaisen. The other children are only playing at being detectives, but Kaisen takes every case seriously. One of the girls also takes an X pill, and her experience is different. Tingting's full name is Yasi Ting, the girl Kudo Sute likes.
