Chinatown

 Chinatown is a 1974 mystery film written by Robert Towne, directed by Roman Polanski and which starred Jack Nicholson, Faye Dunaway, John Huston and Joe Mantell.  

Chinatown was nominated for 11 Academy Awards including Best Picture (won by The Godfather, Part II), Best Director (won by Francis Ford Coppola for The Godfather, Part II), Best Actor (Nicholson, won by Art Carney for Harry and Tonto) and Best Actress (Dunaway, won by Ellen Burstyn for Alice Doesn't Live Here Anymore).   Towne won the film's only Academy Award: for Best Original Screenplay.

In the film Chinatown, a woman in 1937 Los Angeles hires private investigator Jake Gittes (Nicholson) to follow her husband, the chief engineer for the local Water and Power, fearing he's having an affair.  Gittes takes photos of him with a young woman which appear in the next day's newspapers.

Turns out the woman who hired Gittes was an imposter.  The chief engineer's wife, Evelyn (Dunaway), threatens Gittes with a lawsuit.  

Gittes:  You don't have to get tough with me.

Evelyn:  I don't get tough with anyone, Mr. Gittes...my lawyer does.

Later, the chief engineer dies under mysterious circumstances.  Evelyn hires Gittes to investigate what happened to her husband.  He learns that Evelyn's father (Huston), a wealthy and dangerous man, was once a business partner of her husband's.  

Gittes and Evelyn enter into a sexual relationship.  Later, he follows her to a house where he sees Evelyn with the young woman Evelyn's husband was seen with at the beginning of the film.  Gittes demands answers.  

Evelyn: She's my daughter.  

Gittes (slapping her):  I said I want the truth.  

Evelyn:  She's my sister.  She's my daughter.  She's my sister and my daughter.

The police discover the chief engineer was murdered and believe Evelyn the murderer.  Gittes knows it was not her, but her father and tries to protect her from both her father and the police.

In the end, in the Chinatown section of LA, Evelyn attempts to escape with her sister/daughter, but the police kill her.  Gittes is angered, but one of his associates (Mantell) gives the finale a classic line:

Forget it, Jake.  It's Chinatown.

Nineteen years earlier, Mantell (Ang) delivered other memorable lines with Ernest Borgnine (Marty) in the film, Marty:

Ang:  What do you feel like doin' tonight?

Marty:  I don't know, Ang, what do you feel like doin'?