A brilliant debut. Two men and a women on a sailboat on a lake for twenty-four hours. One of the men is married to the woman; the other man is a hitchhiker they picked up. The married man brings the hitchhiker out on the boat as part of a game; the hitchhiker knows it, but goes anyway.
The inevitable sexual tension develops as the men's natural animal rivalry drives them further and further into conflict with one another. But two surprising things happen.
First, although the girl is the obvious fulcrum for their rivalry, she's kept in the background for most of the film (which in itself is a neat trick, considering the close quarters this film takes place in: she's always there, never far away, and yet Polanski manages to place his actors and his camera in such a way as to clearly suggest psychological foreground and background at all times). When she does come to the fore, it's a great revelation, not just of her character but of the hitchhiker's.
Second, the tension doesn't erupt into violence, as we expect it to. Something else happens, a trick, a subterfuge, and instead of getting the big dick-swinging showdown the two men clearly want, we get doubt, uncertainty, hollow victories.
The final shot is perfect, with the married man sitting in his car at a crossroads, unsure which way to turn. If he goes in one direction he's claiming victory over the hitchhiker, keeping his manliness, but turning himself into the police for a crime he may not have committed. If he goes in the other direction he gets to keep his freedom, but at the expense of acknowledging that his wife has cuckolded him. Manhood or freedom?
All of this is fine, but made much finer by the excellent photography. It's not a big boat they're on, and Polanski makes this very restricted space work for him. It gives him a lot of simple variables that he uses to make surprisingly complex, evocative shots. The groupings of the characters, the juxtaposition of people in odd contortions (ducking under booms, etc.) with blank expanses of sail or black lakewater. At times it's almost abstract, but then again it can be very physical, the way Polanski's camera captures all the contours of these three people's flesh. (It helps that this is 1961, and these are real human bodies, not subjected to years of unnatural sculpting and training.)