Underworld novels usually described the protagonist's growth and struggles in the underworld world. These novels usually involved violence, blood, drugs, guns, and other elements. At the same time, there might be complicated interpersonal relationships and conspiracies. The common topics of underworld novels included: gangster culture, gangster history, the growth experience of gang members, the structure and operation of gang organizations, and the struggles and contradictions between gangs. Some famous underworld novels included The Godfather, True Colors of Heroes, Crouching Tiger, Hidden Dragon, and so on.