Based on the novel by Fergus Hume, this is a human story of jealousy, blackmail, self-made men, frustrated ambitions and secrecy. It takes place in Melbourne, Australia, and involves an investigation into a homicide where the deceased was discovered on the inside of a hansom cab. The influential and secretive Frettlby family is at the center of the mystery, and the name of the killer himself is not as much significance in the story, as is the role of the Frettlby family and their secret.