The character Travis Bickle drives a taxi around and complains about all the pimps,pushers,perverts,skunkpussies,prostitutes and lowlifes that trash the streets of the city. He imagines that it needs cleaned up by him being the hero. Then he meets a young prostitute thats like 12 year old (played by Jodi Foster in movie) He don't have sex with her but just talks to her. He feels the street hustler he met earlier is holding a threat over her forcing the minor into prostitution. So he buys two guns an goes into rundown apartment building shooting her pimp and others that work in that building.