A couple pick up a young hitchiker and invite him to come sailing with them. However, things take a turn for the sinister as the husband picks a fight with their new companion.
Having attracted international attention in the early '60s with cruelly absurdist short films (Two Men and a Wardrobe, The Fat and the Lean) about isolated characters clashing as they struggle through empty landscapes, Polanski's first feature elaborates on the theme but with added depth of characterisation. Indeed Knife in the Water is so well-written and acted you don't notice until very late how artificial and stylised the whole set-up is.
The three characters obsessively flirt with each other and play one-upmanship games: pick-up-sticks, knife-throwing, tale-telling, that macho knife-between-the-fingers stunt seen in Aliens, yachtsmanship.
These days, it's likely this story would be resolved by the revelation that one or more of the characters is a serial killer, but back in 1962 Polanski was sure enough of his effects to have the up-front action consist of apparently trivial conversations and contests with all the deep, disturbing character stuff going on below the waterline.
With then-modish and still-effective hand-held black and white photography of ominously calm countryside accompanied by an eerily burbling jazz score from Krysztof Komeda and excellent underplaying (Polanski, deemed not handsome enough to play the teenager himself, dubbed Malanowicz) from all three principles, this remains as fresh and rich as it did on its first release.
You can see the seeds of much of Polanski's later work here, in the only feature he has made in Polish; though he has made deeper, more ambitious movies he has never directed another piece as perfect as this miniature.
Polanski arrived on the scene with an almost super-human knack for tension; one of the great directorial debuts in cinema's history.