HG is set in a futuristic world, in which humans co-exists with androids, highly advanced cybernetic organisms. However, this co-existence is anything but peaceful, since android are going rampant, and a special police force known as ACP ("Anti Criminal-cyborg Police") is specifically assigned to deal with them. Two young and lovely police officers, Angelica and Apple, receive a S.O.S. signal from two army pilots, who were attacked by a mysterious female cyborg who called herself Patricia von Kreuzel. Upon arriving at the crime scene, the heroines find no survivors. Together with their colleague, a young detective named Keith, they must investigate and solve this case.