As two couples are visiting Niagara Falls, tensions between one wife and her husband reach the level of murder.

[Upon seeing Rose Loomis in a low-cut, tight-fitting red dress]
Ray Cutler: Hey, get out the firehose!
[to Polly]
Ray Cutler: Why don't you ever get a dress like that?
Polly Cutler: Listen. For a dress like that, you've got to start laying plans when you're about thirteen.
[First line, voiceover as we watch him at the base of the Falls]
George Loomis: Why should the Falls drag me down here at 5 o'clock in the morning? To show me how big they are and how small I am? To remind me they can get along without any help? All right, so they've proved it. But why not? They've had ten thousand years to get independent. What's so wonderful about that? I suppose I could too, only it might take a little more time.
George Loomis: Let me tell you something. You're young, you're in love. Well, I'll give you a warning. Don't let it get out of hand, like those falls out there. Up above... d'you ever see the river up above the falls? It's calm, and easy, and you throw in a log, it just floats around. Let it move a little further down and it gets going faster, hits some rocks, and... in a minute it's in the lower rapids, and... nothing in the world - including God himself, I suppose - can keep it from going over the edge. It just - goes.
Polly Cutler: Don't worry. I'm one of those logs that just hang around in the calm.
George Loomis: You smell like a dime store. I know what that means.
Rose Loomis: Sure. I'm meeting somebody, just anybody handy, as long as he's a man! How 'bout the ticket seller himself? I could grab him on the way out, or one of the kids with the phonograph. Anybody suits me. Take your pick.
Polly Cutler: Fine thing. I tell him we're on our honeymoon and you drag out a copy of Winston Churchill! He must think I'm a pretty hard article.
Ray Cutler: You should have told him we're on a delayed honeymoon.
Polly Cutler: Delayed or not, we agreed to treat it like a regular one, didn't we?
[quick kiss]
Ray Cutler: I'm game. And it'll be just as good as a regular honeymoon.
Polly Cutler: Well, it should be better. I've got my union card now.
[Lascivious glance]
Customs Officer: How long do you plan to be here?
Ray Cutler: Three days.
Customs Officer: Honeymooners?
Polly Cutler: That's right.
Customs Officer: That isn't liquor you have in that case under your coat, is it?
Ray Cutler: Uh, books. I'm going to catch up on my reading.
Customs Officer: Reading!
George Loomis: Too bad, they can't play it for you now, Rose.
[Polly Cutler catches Rose Loomis in a passionate embrace with her lover]
Polly Cutler: Didn't that Mrs. Loomis say she was going shopping?
Ray Cutler: Yeah. Why?
Polly Cutler: Well, she sure got herself an armful of groceries.