Heiji is asked by Kasukawa to investigate a man who is lurking near the house of Ryoko Morozumi. An arsonist, dubbed the Red Horse after the red horse figurines he leaves behind at the fires, has been burning precincts in order. With the first three having already experienced a fire, and Ryoko's house being on the fourth precinct, they suspect the strange man to be the arosonist. While Kogoro, Conan, and Heiji stalk the house, it catches fire in the middle of the night. There are four suspected to be the arsonist: A salesmen named Takanori Genda, Ryoko's paramour and a Feng shui reader Misao Soga, Ryoko's sister Keiko Gondou, and Ryoko's husband Akira Morozumi. Since the latter three have established alibi's, this leaves Genda as their prime suspect.