Common Sense Note
Parents need to know that this Alfred Hitchcock classic contains several fatal and non-fatal shootings (though barely any blood is shown), plus an inferred strangling and some hand-to-hand fighting, which is more comical than serious. Social drinking (champagne) is fairly frequent, and a plot line revolves around a character possibly getting drugged. There are some don't-try-this-at-home stunts on a moving locomotive.
Scenes of young ladies in their slips. An insulting accusation that one character was born "out of wedlock." Two half-naked men have to share a bed together.
Shootings and a gun battle, with some deaths and wounding, but very little blood. A hand-to-hand scuffle, characters stunned with blows to the head. Inference that a murder will take place in an operating room.
Overall theme, if any, is that things aren't always what (or who) they seem. Even grandmotherly Mrs. Froy isn't the innocent person she claimed to be. Secondary point that the heroine doesn't have to follow through with the security of marriage if the guy seems boring.
Drugs / Tobacco /
Social drinking, with narcotic poison (supposedly) insinuated into liquor glasses, presumably champagne.