Case Closed: Season 1, Episode 658

1 - 658: The Hot Trap in Chocolate

Through Sonoko's contacts, she invites Ran and Conan to attend the pre-opening of a chocolate restaurant managed by the famous chocolatier Yukihiko Tsujimoto. During the presentation, a fire ignites and Tsujimoto burns to death. After Conan investigates, he uses Sonoko to reveal the fire was caused by using a makeshift lithium–air battery; Salt water and the aluminum cups created static electricity which ignited the steel wool and alcoholic vapors. He reveals Mayuko Sakura, the victim's partner, to be the culprit, evidenced by the fact the water was not salted until the presentation began. Sakura confesses and reveals Tsujimoto manipulated her feelings for his own gain and intended to exile her after his success.