Knife in the Water is a 1962 Polish psychological thriller film co-written and directed by Roman Polanski in his feature debut, and starring Leon Niemczyk, Jolanta Umecka, and Zygmunt Malanowicz. Its plot follows a husband and wife who are accompanied on a boating trip by a young male hitchhiker, who spurs a number of escalating confrontations between the couple.

Plot

Andrzej (Leon Niemczyk) and Krystyna (Jolanta Umecka) are driving to a lake to go sailing when they come upon a young man (Zygmunt Malanowicz) hitchhiking in the middle of the road. After nearly hitting him, Andrzej invites the young man along. When they arrive at the lake, instead of leaving the young man behind, Andrzej invites him to go sailing with them. The young man accepts the offer, and, not knowing much about sailing, must learn many hard lessons from Andrzej.