Merry Go Round is set in Yokohama, in year 2197. The city has turned into an international megalopolis, where crime prospers, and where justice is pursued by lone vigilante fighters. The hero of the story is a private detective named Brian. The first case is about an assault on a prostitute in the brothel "John Wayne". Further investigation reveals that the assault is connected to other cases, some of which involve dangerous biological experiments. With the help of the policewoman Akane, the bounty hunter Ridley, and others, Brian begins to gradually see the whole picture...