Conan prevents an accident involving a out-of-control car with no working breaks. Someone poked holes in the brake hose, and the police investigate the incident as an attempted murder. The driver Hosoo was on his way to deliver a valuable double-sided mask to Ichikawa Ebizo, who is rehearsing at the kabuki theater. Ebizo plans to use the mask at next month's performance of "Nanatsu Men."

The ventriloquist Tengan puts on a show about a ventriloquist who becomes possessed by his doll and murders his wife. Tengan falls victim to a genuine split personality disorder, and the personality of his doll appears and orders him to kill his wife Kazuko. The next morning, Kazuko is found murdered. Tengan confesses...