Four university students get the loan of a sailing boat for a cruise on the Darkwater River on the East coast of England. The innocent nautical pleasures of these debutant sailors are harshly interrupted by brutal events that not only terminate their cruise but pursue them afterwards as a menace to their futures and possibly to their lives. With the help of an unexpected ally, they finally decide to act in a radical way. Did they have any other choice? Could they have behaved differently? These questions are likely to haunt them for the rest of their lives.