Detective Conan

Shin'ichi helps solve a murder on a balcony. After-wards Shin'ichi goes with his childhood friend, Ran to an amusement park. When someone is decapitated on a roller coaster, they're riding on, he solves the case quickly. As Shin'ichi and Ran are about to leave, Shin'ichi follows a suspicious man into an alley he is knocked out and give a poison by a man in black, the poison doesn't kill him but instead shrinks him to the size of a kid.