Peeper (1975)

The film is set in Los Angeles in 1947. A criminal (Michael Constantine) on the run from hired killers comes to the office of a private detective named Tucker (Michael Caine) and asks Tucker to find a daughter he left at an orphanage in 1918. The man has a substantial amount of money that he wants to give the girl. Tucker's search leads him to two sisters (Natalie Wood, Kitty Winn), daughters of a rich Beverly Hills widow (Dorothy Adams). Tucker is sure one of the sisters is the man's daughter, but he's not sure which is the right one. Meanwhile, the killers chasing Tucker's client are now chasing the detective, and Tucker also discovers that the widow's brother-in-law (Thayer David) may be blackmailing the two girls and/or embezzling from the widow. Tucker also keeps encountering a mysterious stranger who seems to know more than he admits, and may or may not be working with the brother-in-law. Ultimately everyone ends up on a cruise ship headed to South America and the various mysteries are resolved.