The Big Sleep (1946)

Wealthy and ailing General Sternwood, who has not much time left, hires Private Detective Philip Marlowe to handle a blackmail perpetrated by rare-book seller Arthur Gwynn Geiger against the General's younger daughter, wild Carmen Sternwood, for collection of purported gambling debts. This blackmail is the second such in the General and Carmen's lives in recent history, the first, which the General paid, perpetrated by a man named Joe Brody. That time, it was handled by the General's companion, Irishman Sean Regan, who a month ago left without a word to the now saddened General, with rumors being that Regan has run off with the blonde wife of casino owner Eddie Mars. Not only does Marlowe have a near close encounter of the intimate kind with Carmen at the Sternwood mansion, but he also has an encounter with the General's older daughter, married Vivian Rutledge, equally wild but wiser (i.e. calculating) than her more impetuous younger sister. Vivian's seeming mission in "running into" Marlowe is to discover the nature of the job, her belief that Marlowe was hired to find out what happened to Regan. In his investigation, Marlowe discovers that he has entered a complex web with all the aforementioned players plus a few others which only tangentially seems to be connected to the blackmail for which he was hired to resolve. While the blackmail somewhat resolves itself, Marlowe can't help but continue to investigate in all the other goings-on, partly out of curiosity, and partly to protect his own hide, with a complicating factor being falling for Vivian, which could be problematic if he discovers she is involved with any of the criminal activity he discovers, including murder.

IMDb: https://www.imdb.com/title/tt0038355