The Buttercup Chain plot
"When two people are in love they're a couple. When four people are in love they're the Buttercup Chain."
France and Margaret are first cousins of each other from twin sisters and were also born on the exact same day. As children they were raised as brother and sister. The two have such platonic love for each other that they are almost incapable of loving anyone else. When Margaret travels to London to live with France, he chooses the beautiful Swedish student Fred with the intention of making him become Margaret's lover. For himself he selects the American girl Manny. While they spend their holidays in Spain, the countryside of England and in Sweden, the foursome communicate with each other and try to understand the secret of love.