Maybe the smallest cast of any major feature film, adapted from a play set in a single room, Polanski does a very good job of getting the emotions and motivations of his three characters to deliver the drama.

After the overthrowing of a fascist government in South America, the wife of a diplomat (Weaver) is horrified when he brings home a stranger (Kingsley) who needed a lift and a place to sleep the night - she's convinced he's the brutal SS-like officer who raped and tortured her when she was a political prisoner because of her peace activism. So she takes him hostage, ties him up and the film is a dramatisation of her promising vengeance and trying to make him own up. When she finally does after a harrowing few hours she lets him off - the confession is her vengeance.

It sounds like a weak ending, but it isn't the point. The point is the emotional states of each character working on the other, and the performances alone are enough to make it worth. Sigourney Weaver is at the other side of the acting universe from the post-teen beauty queens who shed their clothes as part of their job description - only a serious, professional director like Polanski could get her to do it. But when she does, she isn't beautiful or attractive naked - the point is her vulnerability, an example of her using her body the way it is to convey her character.