Conan and his friends, along with assistant homeroom teacher Wakasa, discover a skeleton in the old storage shed at the school. The victim died approximately ten years earlier. Ten years ago, a group of four thieves broke into the home of a wealthy man and fled with 200 million yen worth of gold ingots. That same night, a group of suspicious figures were seen entering Teitan Elementary School. Conan and his friends attempt to crack the code written on the headband found in the skeleton`s hand. Conan realizes the class schedule Ayumi found in the storage shed is the key to cracking the code...