Frank Jessup: [of Diane's 'evil' stepmother] ... If she's tryin' to kill you, why did she turn on the gas in her own room first?
Diane Tremayne: ...To make it look as though somebody else were guilty...
Frank Jessup: Is that what you did?
Diane Tremayne: Frank, are you accusing me?
Frank Jessup: I'm not accusing anybody. But if I were a cop, and not a very bright cop at that, I'd say that your story was as phony as a three dollar bill.
Diane Tremayne: ...How can you say that to me?
Frank Jessup: Oh, you mean after all we've been to each other?... Diane, look. I don't pretend to know what goes on behind that pretty little face of yours - I don't *want* to. But I learned one thing very early. Never be the innocent bystander - that's the guy that always gets hurt. If you want to play with matches, that's your business. But not in gas-filled rooms - that's not only dangerous, it's stupid.
Frank Jessup: [to Mary] You know something? You're a pretty nice guy - for a girl.
Mrs. Catherine Tremayne: Charles, at times your charm wears dangerously thin. Right now it's so thin I can see through it.