An early thriller from director Roman Polanski. When a successful sportswriter and his wife invite a strange young boy to join them on their sailboat, the husband, jealous of the boy's youth, continually provokes him, chiding him for his lack of prowess in swimming and sailing. However, the tense atmosphere on board comes to a head when during a quarrel the husband flings the boy's pocket knife into the water. The boy jumps in to retrieve it, but does not re-surface.