Frederic, a student, got himself invited by a Swedish family, living in an isolated castle (hence the title: "a castle in Sweden"). The scene takes place in cold winter, the castle being surrounded by snow. Frederic slowly depicts one after another, each member of that strange family: Hugo, the Castle's master, 40 years old, married to Eleanore whom Frederic begins to be attracted to; Sebastien, Eleanore's incestuous and dandy brother; Agathe, Hugo's old fashioned sister; and Ophelie... Who is Ophelie actually? That is one among several mysteries that Frederic will try to solve out. Who is manipulating whom? Frederic's rising love to Eleanore and the truth about the gorgeous Ophelie will lead to unpredictable consequences. An amazing casting and a mysterious Ophelie give birth on the screen to Sagan's play. I personally didn't like the play but I love this movie.