Because of Mouri's love of horses he takes Conan and Ran to an OK corral ranch. One of their prize winning horses gets spooked and they all go running after her. They reach the horse and Conan finds blood on her horseshoe. They then find the farrier; one who shoes the horses, murdered. They find out that the farrier, had been meeting with a businessman who wanted to buy and ruin breeding any more horses that would save the ranch. Conan deduces that it wasn't an accident and that someone gave the horse chocolate which is stimulant for horses. But it wasn't the cause for the death and was a cover-up for the real criminal. And that the murder weapon was the horseshoe that the person in haste put on wrong. The criminal confesses and had killed the farrier accidentally in self-defense.