Adopted by his rich Uncle Charles and taken to Germany on the death of his parents, the inept British teenager Frank is introduced to the free-wheeling 1970s European lifestyle and begins to fantasise about his uncle's glamorous Italian wife Martha. She seduces Frank and then tries to persuade him to kill her husband so that they can inherit his money. However, though the idea is to drown Charles from a rowing boat, they all fall into the water and she drowns by accident instead, leaving uncle and nephew to resume the friendly relations that she had disrupted.
