The Big Sleep (1946)

P.I. Philip Marlowe's hired by a wealthy general to find out and stop his daughter Carmen from being blackmailed over gambling debts, Marlowe finds himself deep within a web of love triangles, blackmail, murder, gambling, and organized crime. With help from Vivian (another of the general's daughters), Marlowe hatches a plot to free the family from this web and trap the real culprit.